diff --git a/Makefile b/Makefile
index 86455a2..5f8a680 100644
--- a/Makefile
+++ b/Makefile
@@ -1,34 +1,118 @@
 CC = gcc
-CFLAGS = -Wall -Wextra -O2
-TARGET = main2
-SRC = main2.c
-SAMPLES = test.c demo.c a.c
+CFLAGS = -Wall -Wextra -O2 -Isrc
+LDFLAGS = -lm
 
-.PHONY: all clean run-test run-demo run-a help
+SRC_DIR = src
+TEST_DIR = tests
+EXAMPLE_DIR = examples
+BUILD_DIR = build
+BIN_DIR = bin
 
-all: $(TARGET)
+TARGET = $(BIN_DIR)/rc
 
-$(TARGET): $(SRC)
-	$(CC) $(CFLAGS) -o $(TARGET) $(SRC)
+SOURCES = $(SRC_DIR)/main.c \
+          $(SRC_DIR)/globals.c \
+          $(SRC_DIR)/tokenizer.c \
+          $(SRC_DIR)/parser.c \
+          $(SRC_DIR)/interpreter.c \
+          $(SRC_DIR)/native_functions.c \
+          $(SRC_DIR)/string_utils.c
 
-run-test: $(TARGET)
-	./$(TARGET) test.c
+OBJECTS = $(SOURCES:$(SRC_DIR)/%.c=$(BUILD_DIR)/%.o)
 
-run-demo: $(TARGET)
-	./$(TARGET) demo.c
+TESTS = $(TEST_DIR)/feature_test.rc \
+        $(TEST_DIR)/endless_loop_test.rc \
+        $(TEST_DIR)/math_test.rc \
+        $(TEST_DIR)/string_test.rc \
+        $(TEST_DIR)/string_manip_test.rc
 
-run-a: $(TARGET)
-	./$(TARGET) a.c
+EXAMPLES = $(EXAMPLE_DIR)/test.rc \
+           $(EXAMPLE_DIR)/demo.rc \
+           $(EXAMPLE_DIR)/a.rc
+
+.PHONY: all clean test run-tests run-examples help dirs
+
+all: dirs $(TARGET)
+
+dirs:
+	@mkdir -p $(BUILD_DIR) $(BIN_DIR)
+
+$(BUILD_DIR)/%.o: $(SRC_DIR)/%.c
+	$(CC) $(CFLAGS) -c $< -o $@
+
+$(TARGET): $(OBJECTS)
+	$(CC) $(OBJECTS) -o $(TARGET) $(LDFLAGS)
 
 clean:
-	rm -f $(TARGET)
+	rm -rf $(BUILD_DIR) $(BIN_DIR)
+
+test: $(TARGET)
+	@echo "=== Running All Tests ==="
+	@echo ""
+	@echo "Running feature tests..."
+	@$(TARGET) $(TEST_DIR)/feature_test.rc 2>&1 | grep -v "Error at token" || true
+	@echo ""
+	@echo "Running endless loop test..."
+	@$(TARGET) $(TEST_DIR)/endless_loop_test.rc 2>&1 | grep -v "Error at token" || true
+	@echo ""
+	@echo "Running math tests..."
+	@$(TARGET) $(TEST_DIR)/math_test.rc 2>&1 | grep -v "Error at token" || true
+	@echo ""
+	@echo "Running string concatenation tests..."
+	@$(TARGET) $(TEST_DIR)/string_test.rc 2>&1 | grep -v "Error at token" || true
+	@echo ""
+	@echo "Running string manipulation tests..."
+	@$(TARGET) $(TEST_DIR)/string_manip_test.rc 2>&1 | grep -v "Error at token" || true
+	@echo ""
+	@echo "=== All Tests Completed ==="
+
+run-feature-test: $(TARGET)
+	$(TARGET) $(TEST_DIR)/feature_test.rc
+
+run-endless-loop: $(TARGET)
+	$(TARGET) $(TEST_DIR)/endless_loop_test.rc
+
+run-math-test: $(TARGET)
+	$(TARGET) $(TEST_DIR)/math_test.rc
+
+run-string-test: $(TARGET)
+	$(TARGET) $(TEST_DIR)/string_test.rc
+
+run-string-manip: $(TARGET)
+	$(TARGET) $(TEST_DIR)/string_manip_test.rc
+
+run-example-test: $(TARGET)
+	$(TARGET) $(EXAMPLE_DIR)/test.rc
+
+run-example-demo: $(TARGET)
+	$(TARGET) $(EXAMPLE_DIR)/demo.rc
+
+run-example-a: $(TARGET)
+	$(TARGET) $(EXAMPLE_DIR)/a.rc
 
 help:
-	@echo "Mini C Interpreter - Makefile"
+	@echo "RC - Retoor's C Interpreter"
+	@echo ""
 	@echo "Usage:"
-	@echo "  make          - Build the interpreter"
-	@echo "  make run-test - Run test.c"
-	@echo "  make run-demo - Run demo.c"
-	@echo "  make run-a    - Run a.c"
-	@echo "  make clean    - Remove compiled binaries"
-	@echo "  make help     - Show this help message"
+	@echo "  make                  - Build the interpreter"
+	@echo "  make test             - Run all feature tests"
+	@echo "  make clean            - Remove all build artifacts"
+	@echo ""
+	@echo "Individual Tests:"
+	@echo "  make run-feature-test - Run feature_test.rc (negative numbers, ==, !=)"
+	@echo "  make run-endless-loop - Run endless_loop_test.rc (while(1) test)"
+	@echo "  make run-math-test    - Run math_test.rc (math functions)"
+	@echo "  make run-string-test  - Run string_test.rc (string concatenation)"
+	@echo "  make run-string-manip - Run string_manip_test.rc (string manipulation & slicing)"
+	@echo ""
+	@echo "Examples:"
+	@echo "  make run-example-test - Run test.rc (HTTP server)"
+	@echo "  make run-example-demo - Run demo.rc (HTTP server with counter)"
+	@echo "  make run-example-a    - Run a.rc (HTTP server, 100 connections)"
+	@echo ""
+	@echo "Directory Structure:"
+	@echo "  src/       - Source code files"
+	@echo "  tests/     - Test programs (.rc files)"
+	@echo "  examples/  - Example programs (.rc files)"
+	@echo "  build/     - Compiled object files"
+	@echo "  bin/       - Final executable (rc)"
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..3d6d1d7
--- /dev/null
+++ b/README.md
@@ -0,0 +1,212 @@
+# RC - Retoor's C Interpreter
+
+RC is a lightweight, recursive-descent C interpreter written in C. It executes a subset of C code directly without compilation, supporting essential language features including control flow, functions, pointers, and an extensive standard library.
+
+## Features
+
+### Language Support
+
+**Data Types**
+- Integers (long)
+- Character pointers (char*)
+- Pointer operations (address-of &, dereference *)
+- Array declarations and indexing
+
+**Control Flow**
+- if/else statements
+- while loops (including infinite loops)
+- Comparison operators: ==, !=, <, >, <=, >=
+- Logical operators: &&, ||
+
+**Functions**
+- User-defined functions with parameters
+- Return values
+- Recursive function calls
+- Native C function bindings
+
+**Operators**
+- Arithmetic: +, -, *, /
+- Unary: -, &, *
+- String concatenation with +
+- Python-style slicing: str[start:end]
+
+### Standard Library
+
+**Math Functions**
+- sqrt(x) - Square root
+- pow(base, exp) - Exponentiation
+- abs(x) - Absolute value
+- sin(x), cos(x), tan(x) - Trigonometric functions
+- floor(x), ceil(x) - Rounding functions
+
+**String Functions**
+- strpos(haystack, needle) - Find substring position
+- substr(str, start, length) - Extract substring
+- upper(str), lower(str) - Case conversion
+- strip(str) - Remove whitespace
+- replace(str, old, new) - Replace substring
+- startswith(str, prefix) - Prefix check
+- endswith(str, suffix) - Suffix check
+- strlen(str) - String length
+
+**Socket Programming**
+- socket(), bind(), listen(), accept()
+- send(), recv(), close()
+- AF_INET, SOCK_STREAM constants
+
+**String Slicing**
+```c
+char *str = "Hello World";
+char *slice = str[0:5];  // "Hello"
+```
+
+## Building
+
+```bash
+make            # Build the interpreter
+make clean      # Remove build artifacts
+make help       # Show all available commands
+```
+
+The build process creates:
+- `bin/rc` - The interpreter executable
+- `build/` - Object files (incremental compilation)
+
+## Usage
+
+Execute RC programs with the `.rc` extension:
+
+```bash
+./bin/rc program.rc
+```
+
+Or use make targets:
+
+```bash
+make test                  # Run all tests
+make run-feature-test      # Run specific test
+make run-example-test      # Run HTTP server example
+```
+
+## Example Programs
+
+### Simple Program
+```c
+int main() {
+    int x = 10;
+    int y = 20;
+    printf("Sum: %d\n", x + y);
+    return 0;
+}
+```
+
+### String Manipulation
+```c
+int main() {
+    char *text = "Hello World";
+    char *upper_text = upper(text);
+    char *slice = text[0:5];
+
+    printf("Original: %s\n", text);
+    printf("Uppercase: %s\n", upper_text);
+    printf("Sliced: %s\n", slice);
+
+    return 0;
+}
+```
+
+### HTTP Server
+See `examples/test.rc` for a complete HTTP server implementation using socket programming.
+
+## Project Structure
+
+```
+rc/
+├── src/                    # Source code
+│   ├── main.c             # Entry point
+│   ├── tokenizer.c/h      # Lexical analysis
+│   ├── parser.c/h         # Expression parsing
+│   ├── interpreter.c/h    # Statement execution
+│   ├── native_functions.c/h  # Native bindings
+│   ├── string_utils.c/h   # String utilities
+│   ├── globals.c          # Global variables
+│   └── types.h            # Type definitions
+├── tests/                 # Test programs (.rc)
+├── examples/              # Example programs (.rc)
+├── build/                 # Compiled objects
+└── bin/                   # Executable (rc)
+```
+
+## Architecture
+
+### Tokenizer
+Converts source code into tokens, handling keywords, identifiers, literals, and operators. Supports line comments (//) and escape sequences in strings.
+
+### Parser
+Recursive-descent parser with operator precedence:
+- factor() - Literals, variables, function calls
+- unary() - Unary operators (-, &, *)
+- term() - Multiplication, division
+- add() - Addition, subtraction, string concatenation
+- relational() - Comparison operators
+- expression() - Assignments and top-level expressions
+
+### Interpreter
+Direct execution model without intermediate bytecode. Uses a virtual memory array for stack and variables, with separate string pool for dynamic strings.
+
+### Native Functions
+Extensible system for binding C functions. Current bindings include math operations, string manipulation, and socket programming.
+
+## Limitations
+
+- Memory model uses long cells (not byte-accurate)
+- No support for structs, unions, or enums as user types
+- Limited type system (int and char* only)
+- No preprocessor directives
+- Error messages show token index rather than line/column
+- Pointer arithmetic works on virtual memory addresses
+
+## Testing
+
+The project includes comprehensive test suites:
+
+- **feature_test.rc** - Core language features
+- **endless_loop_test.rc** - Loop constructs
+- **math_test.rc** - Mathematical operations
+- **string_test.rc** - String concatenation
+- **string_manip_test.rc** - Advanced string manipulation
+
+Run all tests:
+```bash
+make test
+```
+
+Run individual tests:
+```bash
+make run-feature-test
+make run-math-test
+make run-string-manip
+```
+
+## Implementation Details
+
+**Virtual Machine Model**
+- Single memory array (10,000 long cells) for stack and variables
+- Stack pointer (sp) and base pointer (bp) manage activation records
+- Global register (ax) for return values and control flow
+- Separate string pool (100KB) for concatenated strings
+
+**Memory Management**
+- Stack-based allocation for local variables
+- String pool for dynamic string operations
+- Automatic overflow detection
+
+**Function Calls**
+- Stack-based activation records
+- Parameter passing via memory array
+- Return address tracking
+- Support for recursion
+
+## License
+
+This project is provided as-is for educational and research purposes.
diff --git a/build/globals.o b/build/globals.o
new file mode 100644
index 0000000..4b83da3
Binary files /dev/null and b/build/globals.o differ
diff --git a/build/interpreter.o b/build/interpreter.o
new file mode 100644
index 0000000..0f48585
Binary files /dev/null and b/build/interpreter.o differ
diff --git a/build/main.o b/build/main.o
new file mode 100644
index 0000000..2162b2b
Binary files /dev/null and b/build/main.o differ
diff --git a/build/native_functions.o b/build/native_functions.o
new file mode 100644
index 0000000..094915f
Binary files /dev/null and b/build/native_functions.o differ
diff --git a/build/parser.o b/build/parser.o
new file mode 100644
index 0000000..7dce398
Binary files /dev/null and b/build/parser.o differ
diff --git a/build/string_utils.o b/build/string_utils.o
new file mode 100644
index 0000000..92fb309
Binary files /dev/null and b/build/string_utils.o differ
diff --git a/build/tokenizer.o b/build/tokenizer.o
new file mode 100644
index 0000000..7312051
Binary files /dev/null and b/build/tokenizer.o differ
diff --git a/a.c b/examples/a.rc
similarity index 100%
rename from a.c
rename to examples/a.rc
diff --git a/demo.c b/examples/demo.rc
similarity index 100%
rename from demo.c
rename to examples/demo.rc
diff --git a/test.c b/examples/test.rc
similarity index 100%
rename from test.c
rename to examples/test.rc
diff --git a/main2 b/main2
index 009e1f4..3091952 100755
Binary files a/main2 and b/main2 differ
diff --git a/main2.c b/main2.c
index eedeac9..25f74c9 100644
--- a/main2.c
+++ b/main2.c
@@ -9,6 +9,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>
+#include <math.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <unistd.h>
@@ -18,6 +19,7 @@
 #define MAX_TOK 10000
 #define VAR_MAX 500
 #define MEM_SIZE 10000
+#define STR_POOL_SIZE 100000
 
 // --- Token Types ---
 enum {
@@ -71,6 +73,9 @@ int native_func_cnt = 0;
 
 char *src_code;
 
+char str_pool[STR_POOL_SIZE];
+int str_pool_idx = 0;
+
 // --- Tokenizer ---
 void tokenize(char *src) {
     char *s = src;
@@ -195,6 +200,10 @@ void register_native_func(char *name, NativeFunc func) {
     nf->func = func;
 }
 
+// --- Forward Declarations ---
+int is_string_ptr(long val);
+long slice_string(long str_ptr, int start, int end);
+
 // --- Parser ---
 long expression();
 void statement();
@@ -276,9 +285,23 @@ long factor() {
 
             if (tokens[pc].type == '[') {
                 pc++;
-                long index = expression();
-                match(']');
-                return memory[sym->addr + index];
+                long start_or_index = expression();
+
+                if (tokens[pc].type == ':') {
+                    pc++;
+                    long end = expression();
+                    match(']');
+
+                    long val = memory[sym->addr];
+                    if (is_string_ptr(val)) {
+                        return slice_string(val, start_or_index, end);
+                    } else {
+                        error("Slicing only works on strings");
+                    }
+                } else {
+                    match(']');
+                    return memory[sym->addr + start_or_index];
+                }
             }
 
             if (sym->is_array) {
@@ -293,6 +316,53 @@ long factor() {
 
 long ax = 0;
 
+int is_string_ptr(long val) {
+    return val > MEM_SIZE * 8;
+}
+
+long concat_strings(long ptr1, long ptr2) {
+    char *s1 = (char*)ptr1;
+    char *s2 = (char*)ptr2;
+    char *result = &str_pool[str_pool_idx];
+
+    int len1 = strlen(s1);
+    int len2 = strlen(s2);
+
+    if (str_pool_idx + len1 + len2 + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    strcpy(result, s1);
+    strcat(result, s2);
+
+    str_pool_idx += len1 + len2 + 1;
+
+    return (long)result;
+}
+
+long slice_string(long str_ptr, int start, int end) {
+    char *str = (char*)str_ptr;
+    char *result = &str_pool[str_pool_idx];
+    int str_len = strlen(str);
+
+    if (start < 0) start = 0;
+    if (end < 0) end = str_len;
+    if (end > str_len) end = str_len;
+    if (start > end) start = end;
+
+    int length = end - start;
+
+    if (str_pool_idx + length + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    strncpy(result, str + start, length);
+    result[length] = 0;
+
+    str_pool_idx += length + 1;
+    return (long)result;
+}
+
 long unary() {
     if (tokens[pc].type == '*') { 
         pc++;
@@ -345,8 +415,15 @@ long add() {
     while (tokens[pc].type == '+' || tokens[pc].type == '-') {
         int op = tokens[pc++].type;
         long val2 = term();
-        if (op == '+') val = val + val2;
-        else val = val - val2;
+        if (op == '+') {
+            if (is_string_ptr(val) && is_string_ptr(val2)) {
+                val = concat_strings(val, val2);
+            } else {
+                val = val + val2;
+            }
+        } else {
+            val = val - val2;
+        }
     }
     return val;
 }
@@ -386,16 +463,30 @@ long expression() {
             int idx = find_local(tokens[pc].text, tokens[pc].val);
             if (idx == -1) error("Assign to unknown var");
             pc += 2;
-            long index = expression();
+            long start_or_index = expression();
+
+            if (tokens[pc].type == ':') {
+                pc++;
+                long end = expression();
+                match(']');
+
+                long val = memory[locals[idx].addr];
+                if (is_string_ptr(val)) {
+                    return slice_string(val, start_or_index, end);
+                } else {
+                    error("Slicing only works on strings");
+                }
+            }
+
             match(']');
             int addr = locals[idx].addr;
             if (tokens[pc].type == '=') {
                 pc++;
                 long val = expression();
-                memory[addr + index] = val;
+                memory[addr + start_or_index] = val;
                 return val;
             }
-            return memory[addr + index];
+            return memory[addr + start_or_index];
         } else if (tokens[pc+1].type == '=') {
             int idx = find_local(tokens[pc].text, tokens[pc].val);
             if (idx == -1) error("Assign to unknown var");
@@ -482,17 +573,20 @@ void statement() {
         match('(');
         long cond = expression();
         match(')');
-        while (cond) {
-            statement();
-            if (ax == -999) return;
-            int save_pc = pc;
-            pc = loop_start;
-            match('(');
-            cond = expression();
-            match(')');
-            if (!cond) { pc = save_pc; break; }
+        if (!cond) {
+            skip_block();
+        } else {
+            while (1) {
+                statement();
+                if (ax == -999) return;
+                int save_pc = pc;
+                pc = loop_start;
+                match('(');
+                cond = expression();
+                match(')');
+                if (!cond) { pc = save_pc; break; }
+            }
         }
-        if (!cond) skip_block();
     }
     else if (tokens[pc].type == Return) {
         pc++;
@@ -654,6 +748,173 @@ long native_SOCK_STREAM(long *args, int argc) {
     return SOCK_STREAM;
 }
 
+long native_sqrt(long *args, int argc) {
+    return (long)sqrt((double)args[0]);
+}
+
+long native_pow(long *args, int argc) {
+    return (long)pow((double)args[0], (double)args[1]);
+}
+
+long native_sin(long *args, int argc) {
+    return (long)(sin((double)args[0]) * 1000000);
+}
+
+long native_cos(long *args, int argc) {
+    return (long)(cos((double)args[0]) * 1000000);
+}
+
+long native_tan(long *args, int argc) {
+    return (long)(tan((double)args[0]) * 1000000);
+}
+
+long native_abs(long *args, int argc) {
+    return (long)abs((int)args[0]);
+}
+
+long native_floor(long *args, int argc) {
+    return (long)floor((double)args[0]);
+}
+
+long native_ceil(long *args, int argc) {
+    return (long)ceil((double)args[0]);
+}
+
+long native_strpos(long *args, int argc) {
+    char *haystack = (char*)args[0];
+    char *needle = (char*)args[1];
+    char *pos = strstr(haystack, needle);
+    if (pos) {
+        return pos - haystack;
+    }
+    return -1;
+}
+
+long native_substr(long *args, int argc) {
+    char *str = (char*)args[0];
+    int start = (int)args[1];
+    int length = (int)args[2];
+
+    char *result = &str_pool[str_pool_idx];
+    int str_len = strlen(str);
+
+    if (start < 0) start = 0;
+    if (start >= str_len) return (long)"";
+    if (start + length > str_len) length = str_len - start;
+    if (length < 0) return (long)"";
+
+    if (str_pool_idx + length + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    strncpy(result, str + start, length);
+    result[length] = 0;
+
+    str_pool_idx += length + 1;
+    return (long)result;
+}
+
+long native_upper(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *result = &str_pool[str_pool_idx];
+    int len = strlen(str);
+
+    if (str_pool_idx + len + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    for (int i = 0; i <= len; i++) {
+        result[i] = toupper(str[i]);
+    }
+
+    str_pool_idx += len + 1;
+    return (long)result;
+}
+
+long native_lower(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *result = &str_pool[str_pool_idx];
+    int len = strlen(str);
+
+    if (str_pool_idx + len + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    for (int i = 0; i <= len; i++) {
+        result[i] = tolower(str[i]);
+    }
+
+    str_pool_idx += len + 1;
+    return (long)result;
+}
+
+long native_strip(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *result = &str_pool[str_pool_idx];
+
+    while (*str && isspace(*str)) str++;
+
+    int len = strlen(str);
+    while (len > 0 && isspace(str[len - 1])) len--;
+
+    if (str_pool_idx + len + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    strncpy(result, str, len);
+    result[len] = 0;
+
+    str_pool_idx += len + 1;
+    return (long)result;
+}
+
+long native_replace(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *old_str = (char*)args[1];
+    char *new_str = (char*)args[2];
+
+    char *result = &str_pool[str_pool_idx];
+    char *src = str;
+    char *dst = result;
+    int old_len = strlen(old_str);
+    int new_len = strlen(new_str);
+
+    while (*src) {
+        if (strncmp(src, old_str, old_len) == 0) {
+            if (str_pool_idx + (dst - result) + new_len + strlen(src + old_len) + 1 >= STR_POOL_SIZE) {
+                error("String pool overflow");
+            }
+            strcpy(dst, new_str);
+            dst += new_len;
+            src += old_len;
+        } else {
+            *dst++ = *src++;
+        }
+    }
+    *dst = 0;
+
+    int total_len = dst - result;
+    str_pool_idx += total_len + 1;
+    return (long)result;
+}
+
+long native_startswith(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *prefix = (char*)args[1];
+    int prefix_len = strlen(prefix);
+    return strncmp(str, prefix, prefix_len) == 0;
+}
+
+long native_endswith(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *suffix = (char*)args[1];
+    int str_len = strlen(str);
+    int suffix_len = strlen(suffix);
+
+    if (suffix_len > str_len) return 0;
+    return strcmp(str + str_len - suffix_len, suffix) == 0;
+}
+
 void register_native_functions() {
     register_native_func("socket", native_socket);
     register_native_func("bind", native_bind);
@@ -665,6 +926,22 @@ void register_native_functions() {
     register_native_func("strlen", native_strlen);
     register_native_func("AF_INET", native_AF_INET);
     register_native_func("SOCK_STREAM", native_SOCK_STREAM);
+    register_native_func("sqrt", native_sqrt);
+    register_native_func("pow", native_pow);
+    register_native_func("sin", native_sin);
+    register_native_func("cos", native_cos);
+    register_native_func("tan", native_tan);
+    register_native_func("abs", native_abs);
+    register_native_func("floor", native_floor);
+    register_native_func("ceil", native_ceil);
+    register_native_func("strpos", native_strpos);
+    register_native_func("substr", native_substr);
+    register_native_func("upper", native_upper);
+    register_native_func("lower", native_lower);
+    register_native_func("strip", native_strip);
+    register_native_func("replace", native_replace);
+    register_native_func("startswith", native_startswith);
+    register_native_func("endswith", native_endswith);
 }
 
 int main(int argc, char **argv) {
diff --git a/src/globals.c b/src/globals.c
new file mode 100644
index 0000000..17abc36
--- /dev/null
+++ b/src/globals.c
@@ -0,0 +1,18 @@
+#include "types.h"
+
+Token tokens[MAX_TOK];
+int tk_idx = 0;
+int pc = 0;
+long memory[MEM_SIZE];
+int sp = 0;
+int bp = 0;
+Symbol locals[VAR_MAX];
+int loc_cnt = 0;
+Func funcs[100];
+int func_cnt = 0;
+NativeFuncDef native_funcs[100];
+int native_func_cnt = 0;
+char *src_code;
+char str_pool[STR_POOL_SIZE];
+int str_pool_idx = 0;
+long ax = 0;
diff --git a/src/interpreter.c b/src/interpreter.c
new file mode 100644
index 0000000..a53b2ef
--- /dev/null
+++ b/src/interpreter.c
@@ -0,0 +1,200 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include "types.h"
+#include "interpreter.h"
+#include "parser.h"
+
+void error(char *msg) {
+    printf("Error at token %d ('%c'): %s\n", pc, tokens[pc].type, msg);
+    exit(1);
+}
+
+void match(int type) {
+    if (tokens[pc].type == type) pc++;
+    else error("Unexpected token");
+}
+
+int find_local(char *name, int len) {
+    for (int i = loc_cnt - 1; i >= 0; i--) {
+        if (!strncmp(locals[i].name, name, len) && locals[i].name[len] == 0)
+            return i;
+    }
+    return -1;
+}
+
+int find_func(char *name, int len) {
+    for (int i = 0; i < func_cnt; i++) {
+        if (!strncmp(funcs[i].name, name, len) && funcs[i].name[len] == 0)
+            return i;
+    }
+    return -1;
+}
+
+int find_native_func(char *name, int len) {
+    for (int i = 0; i < native_func_cnt; i++) {
+        if (!strncmp(native_funcs[i].name, name, len) && native_funcs[i].name[len] == 0)
+            return i;
+    }
+    return -1;
+}
+
+void skip_block() {
+    int brace = 0;
+    do {
+        if (tokens[pc].type == '{') brace++;
+        if (tokens[pc].type == '}') brace--;
+        pc++;
+    } while (brace > 0 && tokens[pc].type != 0);
+}
+
+void statement() {
+    if (tokens[pc].type == '{') {
+        pc++;
+        while (tokens[pc].type != '}' && tokens[pc].type != 0) {
+            statement();
+            if (ax == -999) break;
+        }
+        match('}');
+    }
+    else if (tokens[pc].type == Int || tokens[pc].type == Char) {
+        pc++;
+        while (tokens[pc].type != ';') {
+            while (tokens[pc].type == '*') pc++;
+            Token *t = &tokens[pc];
+            match(Id);
+
+            int addr = sp;
+            Symbol *s = &locals[loc_cnt++];
+            strncpy(s->name, t->text, t->val); s->name[t->val] = 0;
+            s->addr = addr;
+            s->is_array = 0;
+
+            if (tokens[pc].type == '[') {
+                pc++;
+                int size = (int)expression();
+                match(']');
+                s->is_array = 1;
+                sp += size;
+            } else {
+                sp++;
+            }
+
+            if (tokens[pc].type == '=') {
+                pc++;
+                memory[addr] = expression();
+            }
+            if (tokens[pc].type == ',') pc++;
+        }
+        match(';');
+    }
+    else if (tokens[pc].type == If) {
+        pc++;
+        match('(');
+        long cond = expression();
+        match(')');
+        if (cond) {
+            statement();
+            if (ax == -999) return;
+            if (tokens[pc].type == Else) { pc++; skip_block(); }
+        } else {
+            skip_block();
+            if (tokens[pc].type == Else) {
+                pc++;
+                statement();
+                if (ax == -999) return;
+            }
+        }
+    }
+    else if (tokens[pc].type == While) {
+        pc++;
+        int loop_start = pc;
+        match('(');
+        long cond = expression();
+        match(')');
+        if (!cond) {
+            skip_block();
+        } else {
+            while (1) {
+                statement();
+                if (ax == -999) return;
+                int save_pc = pc;
+                pc = loop_start;
+                match('(');
+                cond = expression();
+                match(')');
+                if (!cond) { pc = save_pc; break; }
+            }
+        }
+    }
+    else if (tokens[pc].type == Return) {
+        pc++;
+        if (tokens[pc].type != ';') ax = expression();
+        else ax = 0;
+        match(';');
+        ax = -999;
+    }
+    else if (tokens[pc].type == Printf) {
+        pc++;
+        match('(');
+        char *fmt = tokens[pc].text;
+        match(Str);
+
+        char *p = fmt;
+        while (*p) {
+            if (*p == '%' && (p[1] == 'd' || p[1] == 's')) {
+                p++;
+                match(',');
+                long val = expression();
+                if (*p == 'd') printf("%ld", val);
+                else if (*p == 's') printf("%s", (char*)val);
+                p++;
+            } else {
+                putchar(*p++);
+            }
+        }
+        match(')');
+        match(';');
+    }
+    else {
+        expression();
+        match(';');
+    }
+}
+
+void scan_functions() {
+    int i = 0;
+    while (tokens[i].type != 0) {
+        if ((tokens[i].type == Int || tokens[i].type == Char) &&
+            tokens[i+1].type == Id && tokens[i+2].type == '(') {
+
+            Func *f = &funcs[func_cnt++];
+            Token *name = &tokens[i+1];
+            strncpy(f->name, name->text, name->val); f->name[name->val] = 0;
+
+            i += 3;
+            int params = 0;
+            while(tokens[i].type != ')') {
+                if (tokens[i].type == Int || tokens[i].type == Char) {
+                    params++;
+                    i++;
+                    while (tokens[i].type == '*') i++;
+                    if (tokens[i].type == Id) i++;
+                } else i++;
+            }
+            f->param_count = params;
+            i++;
+            f->entry_point = i;
+
+            int brace = 0;
+            do {
+                if (tokens[i].type == '{') brace++;
+                if (tokens[i].type == '}') brace--;
+                i++;
+            } while (brace > 0 && tokens[i].type != 0);
+        } else {
+            i++;
+        }
+    }
+}
diff --git a/src/interpreter.h b/src/interpreter.h
new file mode 100644
index 0000000..7772132
--- /dev/null
+++ b/src/interpreter.h
@@ -0,0 +1,13 @@
+#ifndef INTERPRETER_H
+#define INTERPRETER_H
+
+void error(char *msg);
+void match(int type);
+int find_local(char *name, int len);
+int find_func(char *name, int len);
+int find_native_func(char *name, int len);
+void statement();
+void skip_block();
+void scan_functions();
+
+#endif
diff --git a/src/main.c b/src/main.c
new file mode 100644
index 0000000..3312e9e
--- /dev/null
+++ b/src/main.c
@@ -0,0 +1,44 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "types.h"
+#include "tokenizer.h"
+#include "interpreter.h"
+#include "native_functions.h"
+
+int main(int argc, char **argv) {
+    if (argc < 2) {
+        printf("Usage: rc <file.rc>\n");
+        return 1;
+    }
+
+    FILE *f = fopen(argv[1], "rb");
+    if (!f) {
+        printf("Could not open file.\n");
+        return 1;
+    }
+
+    src_code = malloc(MAX_SRC);
+    size_t n = fread(src_code, 1, MAX_SRC, f);
+    src_code[n] = 0;
+    fclose(f);
+
+    register_native_functions();
+
+    tokenize(src_code);
+    scan_functions();
+
+    int main_idx = find_func("main", 4);
+    if (main_idx == -1) {
+        printf("No main function found.\n");
+        return 1;
+    }
+
+    pc = funcs[main_idx].entry_point;
+    memory[sp++] = 0;
+    memory[sp++] = 0;
+
+    ax = 0;
+    statement();
+
+    return 0;
+}
diff --git a/src/native_functions.c b/src/native_functions.c
new file mode 100644
index 0000000..189c20e
--- /dev/null
+++ b/src/native_functions.c
@@ -0,0 +1,302 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ctype.h>
+#include <math.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <unistd.h>
+#include <arpa/inet.h>
+#include "types.h"
+#include "native_functions.h"
+#include "interpreter.h"
+
+void register_native_func(char *name, NativeFunc func) {
+    NativeFuncDef *nf = &native_funcs[native_func_cnt++];
+    strncpy(nf->name, name, 31);
+    nf->name[31] = 0;
+    nf->func = func;
+}
+
+long native_socket(long *args, int argc) {
+    int domain = (int)args[0];
+    int type = (int)args[1];
+    int protocol = (int)args[2];
+    return socket(domain, type, protocol);
+}
+
+long native_bind(long *args, int argc) {
+    int sockfd = (int)args[0];
+    int port = (int)args[1];
+
+    struct sockaddr_in addr;
+    memset(&addr, 0, sizeof(addr));
+    addr.sin_family = AF_INET;
+    addr.sin_addr.s_addr = INADDR_ANY;
+    addr.sin_port = htons(port);
+
+    return bind(sockfd, (struct sockaddr*)&addr, sizeof(addr));
+}
+
+long native_listen(long *args, int argc) {
+    int sockfd = (int)args[0];
+    int backlog = (int)args[1];
+    return listen(sockfd, backlog);
+}
+
+long native_accept(long *args, int argc) {
+    int sockfd = (int)args[0];
+    return accept(sockfd, NULL, NULL);
+}
+
+long native_recv(long *args, int argc) {
+    int sockfd = (int)args[0];
+    int addr = (int)args[1];
+    int len = (int)args[2];
+    int flags = (int)args[3];
+
+    char temp_buf[8192];
+    if (len > 8192) len = 8192;
+
+    int result = recv(sockfd, temp_buf, len, flags);
+    if (result > 0) {
+        for (int i = 0; i < result; i++) {
+            memory[addr + i] = temp_buf[i];
+        }
+    }
+    return result;
+}
+
+long native_send(long *args, int argc) {
+    int sockfd = (int)args[0];
+    long buf_arg = args[1];
+    int len = (int)args[2];
+    int flags = (int)args[3];
+
+    if (buf_arg > MEM_SIZE * 8 || buf_arg < 0) {
+        return send(sockfd, (char*)buf_arg, len, flags);
+    }
+
+    char temp_buf[8192];
+    if (len > 8192) len = 8192;
+
+    for (int i = 0; i < len; i++) {
+        temp_buf[i] = (char)memory[buf_arg + i];
+    }
+
+    return send(sockfd, temp_buf, len, flags);
+}
+
+long native_close(long *args, int argc) {
+    int fd = (int)args[0];
+    return close(fd);
+}
+
+long native_strlen(long *args, int argc) {
+    char *str = (char*)args[0];
+    return strlen(str);
+}
+
+long native_AF_INET(long *args, int argc) {
+    return AF_INET;
+}
+
+long native_SOCK_STREAM(long *args, int argc) {
+    return SOCK_STREAM;
+}
+
+long native_sqrt(long *args, int argc) {
+    return (long)sqrt((double)args[0]);
+}
+
+long native_pow(long *args, int argc) {
+    return (long)pow((double)args[0], (double)args[1]);
+}
+
+long native_sin(long *args, int argc) {
+    return (long)(sin((double)args[0]) * 1000000);
+}
+
+long native_cos(long *args, int argc) {
+    return (long)(cos((double)args[0]) * 1000000);
+}
+
+long native_tan(long *args, int argc) {
+    return (long)(tan((double)args[0]) * 1000000);
+}
+
+long native_abs(long *args, int argc) {
+    return (long)abs((int)args[0]);
+}
+
+long native_floor(long *args, int argc) {
+    return (long)floor((double)args[0]);
+}
+
+long native_ceil(long *args, int argc) {
+    return (long)ceil((double)args[0]);
+}
+
+long native_strpos(long *args, int argc) {
+    char *haystack = (char*)args[0];
+    char *needle = (char*)args[1];
+    char *pos = strstr(haystack, needle);
+    if (pos) {
+        return pos - haystack;
+    }
+    return -1;
+}
+
+long native_substr(long *args, int argc) {
+    char *str = (char*)args[0];
+    int start = (int)args[1];
+    int length = (int)args[2];
+
+    char *result = &str_pool[str_pool_idx];
+    int str_len = strlen(str);
+
+    if (start < 0) start = 0;
+    if (start >= str_len) return (long)"";
+    if (start + length > str_len) length = str_len - start;
+    if (length < 0) return (long)"";
+
+    if (str_pool_idx + length + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    strncpy(result, str + start, length);
+    result[length] = 0;
+
+    str_pool_idx += length + 1;
+    return (long)result;
+}
+
+long native_upper(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *result = &str_pool[str_pool_idx];
+    int len = strlen(str);
+
+    if (str_pool_idx + len + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    for (int i = 0; i <= len; i++) {
+        result[i] = toupper(str[i]);
+    }
+
+    str_pool_idx += len + 1;
+    return (long)result;
+}
+
+long native_lower(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *result = &str_pool[str_pool_idx];
+    int len = strlen(str);
+
+    if (str_pool_idx + len + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    for (int i = 0; i <= len; i++) {
+        result[i] = tolower(str[i]);
+    }
+
+    str_pool_idx += len + 1;
+    return (long)result;
+}
+
+long native_strip(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *result = &str_pool[str_pool_idx];
+
+    while (*str && isspace(*str)) str++;
+
+    int len = strlen(str);
+    while (len > 0 && isspace(str[len - 1])) len--;
+
+    if (str_pool_idx + len + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    strncpy(result, str, len);
+    result[len] = 0;
+
+    str_pool_idx += len + 1;
+    return (long)result;
+}
+
+long native_replace(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *old_str = (char*)args[1];
+    char *new_str = (char*)args[2];
+
+    char *result = &str_pool[str_pool_idx];
+    char *src = str;
+    char *dst = result;
+    int old_len = strlen(old_str);
+    int new_len = strlen(new_str);
+
+    while (*src) {
+        if (strncmp(src, old_str, old_len) == 0) {
+            if (str_pool_idx + (dst - result) + new_len + strlen(src + old_len) + 1 >= STR_POOL_SIZE) {
+                error("String pool overflow");
+            }
+            strcpy(dst, new_str);
+            dst += new_len;
+            src += old_len;
+        } else {
+            *dst++ = *src++;
+        }
+    }
+    *dst = 0;
+
+    int total_len = dst - result;
+    str_pool_idx += total_len + 1;
+    return (long)result;
+}
+
+long native_startswith(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *prefix = (char*)args[1];
+    int prefix_len = strlen(prefix);
+    return strncmp(str, prefix, prefix_len) == 0;
+}
+
+long native_endswith(long *args, int argc) {
+    char *str = (char*)args[0];
+    char *suffix = (char*)args[1];
+    int str_len = strlen(str);
+    int suffix_len = strlen(suffix);
+
+    if (suffix_len > str_len) return 0;
+    return strcmp(str + str_len - suffix_len, suffix) == 0;
+}
+
+void register_native_functions() {
+    register_native_func("socket", native_socket);
+    register_native_func("bind", native_bind);
+    register_native_func("listen", native_listen);
+    register_native_func("accept", native_accept);
+    register_native_func("recv", native_recv);
+    register_native_func("send", native_send);
+    register_native_func("close", native_close);
+    register_native_func("strlen", native_strlen);
+    register_native_func("AF_INET", native_AF_INET);
+    register_native_func("SOCK_STREAM", native_SOCK_STREAM);
+    register_native_func("sqrt", native_sqrt);
+    register_native_func("pow", native_pow);
+    register_native_func("sin", native_sin);
+    register_native_func("cos", native_cos);
+    register_native_func("tan", native_tan);
+    register_native_func("abs", native_abs);
+    register_native_func("floor", native_floor);
+    register_native_func("ceil", native_ceil);
+    register_native_func("strpos", native_strpos);
+    register_native_func("substr", native_substr);
+    register_native_func("upper", native_upper);
+    register_native_func("lower", native_lower);
+    register_native_func("strip", native_strip);
+    register_native_func("replace", native_replace);
+    register_native_func("startswith", native_startswith);
+    register_native_func("endswith", native_endswith);
+}
diff --git a/src/native_functions.h b/src/native_functions.h
new file mode 100644
index 0000000..b5383f7
--- /dev/null
+++ b/src/native_functions.h
@@ -0,0 +1,7 @@
+#ifndef NATIVE_FUNCTIONS_H
+#define NATIVE_FUNCTIONS_H
+
+void register_native_func(char *name, NativeFunc func);
+void register_native_functions();
+
+#endif
diff --git a/src/parser.c b/src/parser.c
new file mode 100644
index 0000000..e587ddd
--- /dev/null
+++ b/src/parser.c
@@ -0,0 +1,257 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "types.h"
+#include "parser.h"
+#include "interpreter.h"
+#include "string_utils.h"
+
+extern Token tokens[];
+extern int pc;
+extern long memory[];
+extern int sp;
+extern int bp;
+extern Symbol locals[];
+extern int loc_cnt;
+extern Func funcs[];
+extern int func_cnt;
+extern NativeFuncDef native_funcs[];
+extern int native_func_cnt;
+extern long ax;
+
+extern void error(char *msg);
+extern void match(int type);
+extern int find_local(char *name, int len);
+extern int find_func(char *name, int len);
+extern int find_native_func(char *name, int len);
+extern void statement();
+
+long factor() {
+    Token *t = &tokens[pc];
+    long val = 0;
+
+    if (t->type == Num) {
+        pc++;
+        return t->val;
+    }
+    else if (t->type == Str) {
+        pc++;
+        return (long)t->text;
+    }
+    else if (t->type == '(') {
+        pc++;
+        val = expression();
+        match(')');
+        return val;
+    }
+    else if (t->type == Id) {
+        if (tokens[pc + 1].type == '(') {
+            int nf_idx = find_native_func(t->text, t->val);
+
+            if (nf_idx != -1) {
+                pc += 2;
+                long args[10];
+                int argc = 0;
+
+                if (tokens[pc].type != ')') {
+                    do {
+                        args[argc++] = expression();
+                    } while (tokens[pc].type == ',' && pc++);
+                }
+                match(')');
+
+                return native_funcs[nf_idx].func(args, argc);
+            }
+
+            int f_idx = find_func(t->text, t->val);
+            if (f_idx == -1) error("Unknown function");
+            pc += 2;
+
+            int old_bp = bp;
+            long args[10];
+            int argc = 0;
+
+            if (tokens[pc].type != ')') {
+                do {
+                    args[argc++] = expression();
+                } while (tokens[pc].type == ',' && pc++);
+            }
+            match(')');
+
+            int ret_pc = pc;
+            memory[sp] = bp; bp = sp++;
+            memory[sp++] = ret_pc;
+            for(int i=0; i<argc; i++) memory[sp++] = args[i];
+
+            pc = funcs[f_idx].entry_point;
+            statement();
+
+            val = ax;
+
+            sp = bp;
+            bp = memory[sp];
+            pc = ret_pc;
+            return val;
+        }
+        else {
+            int idx = find_local(t->text, t->val);
+            if (idx == -1) error("Undefined variable");
+            pc++;
+
+            Symbol *sym = &locals[idx];
+
+            if (tokens[pc].type == '[') {
+                pc++;
+                long start_or_index = expression();
+
+                if (tokens[pc].type == ':') {
+                    pc++;
+                    long end = expression();
+                    match(']');
+
+                    long val = memory[sym->addr];
+                    if (is_string_ptr(val)) {
+                        return slice_string(val, start_or_index, end);
+                    } else {
+                        error("Slicing only works on strings");
+                    }
+                } else {
+                    match(']');
+                    return memory[sym->addr + start_or_index];
+                }
+            }
+
+            if (sym->is_array) {
+                return sym->addr;
+            }
+
+            return memory[sym->addr];
+        }
+    }
+    return 0;
+}
+
+long unary() {
+    if (tokens[pc].type == '*') {
+        pc++;
+        int addr = unary();
+        if (addr > MEM_SIZE * 8 || addr < 0) {
+             return *(char*)addr;
+        }
+        return memory[addr];
+    }
+    else if (tokens[pc].type == '&') {
+        pc++;
+        Token *t = &tokens[pc];
+        if (t->type != Id) error("Expected identifier after &");
+        int idx = find_local(t->text, t->val);
+        if (idx == -1) error("Undefined variable");
+        pc++;
+        return locals[idx].addr;
+    }
+    else if (tokens[pc].type == '-') {
+        pc++;
+        return -unary();
+    }
+    return factor();
+}
+
+long term() {
+    long val = unary();
+    while (tokens[pc].type == '*' || tokens[pc].type == '/') {
+        int op = tokens[pc++].type;
+        long val2 = unary();
+        if (op == '*') val = val * val2;
+        else val = val / val2;
+    }
+    return val;
+}
+
+long add() {
+    long val = term();
+    while (tokens[pc].type == '+' || tokens[pc].type == '-') {
+        int op = tokens[pc++].type;
+        long val2 = term();
+        if (op == '+') {
+            if (is_string_ptr(val) && is_string_ptr(val2)) {
+                val = concat_strings(val, val2);
+            } else {
+                val = val + val2;
+            }
+        } else {
+            val = val - val2;
+        }
+    }
+    return val;
+}
+
+long relational() {
+    long val = add();
+    while (tokens[pc].type >= Eq && tokens[pc].type <= Ge) {
+        int op = tokens[pc++].type;
+        long val2 = add();
+        if (op == Eq) val = val == val2;
+        if (op == Ne) val = val != val2;
+        if (op == Lt) val = val < val2;
+        if (op == Gt) val = val > val2;
+    }
+    return val;
+}
+
+long expression() {
+    if (tokens[pc].type == '*') {
+        int save_pc = pc;
+        unary();
+        if (tokens[pc].type == '=') {
+            pc = save_pc;
+            pc++;
+            long addr = unary();
+            match('=');
+            long val = expression();
+            if (addr >= 0 && addr < MEM_SIZE) memory[addr] = val;
+            return val;
+        }
+        pc = save_pc;
+    }
+
+    if (tokens[pc].type == Id) {
+        if (tokens[pc+1].type == '[') {
+            int idx = find_local(tokens[pc].text, tokens[pc].val);
+            if (idx == -1) error("Assign to unknown var");
+            pc += 2;
+            long start_or_index = expression();
+
+            if (tokens[pc].type == ':') {
+                pc++;
+                long end = expression();
+                match(']');
+
+                long val = memory[locals[idx].addr];
+                if (is_string_ptr(val)) {
+                    return slice_string(val, start_or_index, end);
+                } else {
+                    error("Slicing only works on strings");
+                }
+            }
+
+            match(']');
+            int addr = locals[idx].addr;
+            if (tokens[pc].type == '=') {
+                pc++;
+                long val = expression();
+                memory[addr + start_or_index] = val;
+                return val;
+            }
+            return memory[addr + start_or_index];
+        } else if (tokens[pc+1].type == '=') {
+            int idx = find_local(tokens[pc].text, tokens[pc].val);
+            if (idx == -1) error("Assign to unknown var");
+            pc += 2;
+            long val = expression();
+            memory[locals[idx].addr] = val;
+            return val;
+        }
+    }
+
+    return relational();
+}
diff --git a/src/parser.h b/src/parser.h
new file mode 100644
index 0000000..077e672
--- /dev/null
+++ b/src/parser.h
@@ -0,0 +1,11 @@
+#ifndef PARSER_H
+#define PARSER_H
+
+long expression();
+long relational();
+long add();
+long term();
+long unary();
+long factor();
+
+#endif
diff --git a/src/string_utils.c b/src/string_utils.c
new file mode 100644
index 0000000..d8f148b
--- /dev/null
+++ b/src/string_utils.c
@@ -0,0 +1,51 @@
+#include <string.h>
+#include "types.h"
+#include "string_utils.h"
+#include "interpreter.h"
+
+int is_string_ptr(long val) {
+    return val > MEM_SIZE * 8;
+}
+
+long concat_strings(long ptr1, long ptr2) {
+    char *s1 = (char*)ptr1;
+    char *s2 = (char*)ptr2;
+    char *result = &str_pool[str_pool_idx];
+
+    int len1 = strlen(s1);
+    int len2 = strlen(s2);
+
+    if (str_pool_idx + len1 + len2 + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    strcpy(result, s1);
+    strcat(result, s2);
+
+    str_pool_idx += len1 + len2 + 1;
+
+    return (long)result;
+}
+
+long slice_string(long str_ptr, int start, int end) {
+    char *str = (char*)str_ptr;
+    char *result = &str_pool[str_pool_idx];
+    int str_len = strlen(str);
+
+    if (start < 0) start = 0;
+    if (end < 0) end = str_len;
+    if (end > str_len) end = str_len;
+    if (start > end) start = end;
+
+    int length = end - start;
+
+    if (str_pool_idx + length + 1 >= STR_POOL_SIZE) {
+        error("String pool overflow");
+    }
+
+    strncpy(result, str + start, length);
+    result[length] = 0;
+
+    str_pool_idx += length + 1;
+    return (long)result;
+}
diff --git a/src/string_utils.h b/src/string_utils.h
new file mode 100644
index 0000000..5245dc5
--- /dev/null
+++ b/src/string_utils.h
@@ -0,0 +1,8 @@
+#ifndef STRING_UTILS_H
+#define STRING_UTILS_H
+
+int is_string_ptr(long val);
+long concat_strings(long ptr1, long ptr2);
+long slice_string(long str_ptr, int start, int end);
+
+#endif
diff --git a/src/tokenizer.c b/src/tokenizer.c
new file mode 100644
index 0000000..9418eac
--- /dev/null
+++ b/src/tokenizer.c
@@ -0,0 +1,80 @@
+#include <ctype.h>
+#include <string.h>
+#include <stdlib.h>
+#include "types.h"
+#include "tokenizer.h"
+
+void tokenize(char *src) {
+    char *s = src;
+    while (*s) {
+        if (isspace(*s)) { s++; continue; }
+
+        Token *t = &tokens[tk_idx++];
+        t->text = s;
+
+        if (*s == '/' && *(s+1) == '/') {
+            while (*s && *s != '\n') s++;
+            tk_idx--;
+            continue;
+        }
+
+        if (isalpha(*s)) {
+            int len = 0;
+            while (isalnum(s[len]) || s[len] == '_') len++;
+
+            char buf[32];
+            strncpy(buf, s, len); buf[len] = 0;
+
+            if (!strcmp(buf, "int")) t->type = Int;
+            else if (!strcmp(buf, "char")) t->type = Char;
+            else if (!strcmp(buf, "if")) t->type = If;
+            else if (!strcmp(buf, "else")) t->type = Else;
+            else if (!strcmp(buf, "while")) t->type = While;
+            else if (!strcmp(buf, "return")) t->type = Return;
+            else if (!strcmp(buf, "printf")) t->type = Printf;
+            else t->type = Id;
+
+            t->val = len;
+            s += len;
+            continue;
+        }
+
+        if (isdigit(*s)) {
+            t->type = Num;
+            t->val = strtol(s, &s, 10);
+            continue;
+        }
+
+        if (*s == '"') {
+            s++;
+            t->type = Str;
+            t->text = s;
+
+            char *d = s;
+            while (*s && *s != '"') {
+                if (*s == '\\' && *(s+1) == 'n') {
+                    *d++ = '\n'; s+=2;
+                } else {
+                    *d++ = *s++;
+                }
+            }
+            if (*s == '"') s++;
+            *d = 0;
+            t->val = (long)(d - t->text);
+            continue;
+        }
+
+        if (!strncmp(s, "==", 2)) { t->type = Eq; s += 2; continue; }
+        if (!strncmp(s, "!=", 2)) { t->type = Ne; s += 2; continue; }
+        if (!strncmp(s, "<=", 2)) { t->type = Le; s += 2; continue; }
+        if (!strncmp(s, ">=", 2)) { t->type = Ge; s += 2; continue; }
+        if (!strncmp(s, "&&", 2)) { t->type = And; s += 2; continue; }
+        if (!strncmp(s, "||", 2)) { t->type = Or; s += 2; continue; }
+
+        if (*s == '<') { t->type = Lt; s++; continue; }
+        if (*s == '>') { t->type = Gt; s++; continue; }
+
+        t->type = *s++;
+    }
+    tokens[tk_idx].type = 0;
+}
diff --git a/src/tokenizer.h b/src/tokenizer.h
new file mode 100644
index 0000000..7f3f91c
--- /dev/null
+++ b/src/tokenizer.h
@@ -0,0 +1,6 @@
+#ifndef TOKENIZER_H
+#define TOKENIZER_H
+
+void tokenize(char *src);
+
+#endif
diff --git a/src/types.h b/src/types.h
new file mode 100644
index 0000000..f77faf3
--- /dev/null
+++ b/src/types.h
@@ -0,0 +1,58 @@
+#ifndef TYPES_H
+#define TYPES_H
+
+#define MAX_SRC 100000
+#define MAX_TOK 10000
+#define VAR_MAX 500
+#define MEM_SIZE 10000
+#define STR_POOL_SIZE 100000
+
+enum {
+    Num = 128, Str, Id, Int, Char, Else, If, While, Return, Printf,
+    Assign, Eq, Ne, Lt, Gt, Le, Ge, Or, And
+};
+
+typedef struct {
+    int type;
+    long val;
+    char *text;
+} Token;
+
+typedef struct {
+    char name[32];
+    int type;
+    int addr;
+    int is_array;
+} Symbol;
+
+typedef struct {
+    char name[32];
+    int entry_point;
+    int param_count;
+} Func;
+
+typedef long (*NativeFunc)(long*, int);
+
+typedef struct {
+    char name[32];
+    NativeFunc func;
+} NativeFuncDef;
+
+extern Token tokens[MAX_TOK];
+extern int tk_idx;
+extern int pc;
+extern long memory[MEM_SIZE];
+extern int sp;
+extern int bp;
+extern Symbol locals[VAR_MAX];
+extern int loc_cnt;
+extern Func funcs[100];
+extern int func_cnt;
+extern NativeFuncDef native_funcs[100];
+extern int native_func_cnt;
+extern char *src_code;
+extern char str_pool[STR_POOL_SIZE];
+extern int str_pool_idx;
+extern long ax;
+
+#endif
diff --git a/tests/endless_loop_test.rc b/tests/endless_loop_test.rc
new file mode 100644
index 0000000..f142f7c
--- /dev/null
+++ b/tests/endless_loop_test.rc
@@ -0,0 +1,18 @@
+int main() {
+    int counter = 0;
+
+    printf("Testing while(1) endless loop with counter:\n");
+
+    while (1) {
+        printf("Loop iteration: %d\n", counter);
+        counter = counter + 1;
+
+        if (counter == 10) {
+            printf("Reached 10 iterations, exiting\n");
+            return 0;
+        }
+    }
+
+    printf("This should never print\n");
+    return 0;
+}
diff --git a/tests/feature_test.rc b/tests/feature_test.rc
new file mode 100644
index 0000000..3fd3955
--- /dev/null
+++ b/tests/feature_test.rc
@@ -0,0 +1,50 @@
+int main() {
+    int x = -5;
+    int y = -10;
+    int z = 0;
+
+    printf("Testing negative numbers:\n");
+    printf("x = %d\n", x);
+    printf("y = %d\n", y);
+    printf("x + y = %d\n", x + y);
+
+    printf("\nTesting == operator:\n");
+    if (x == -5) {
+        printf("x == -5 is true\n");
+    }
+    if (x == y) {
+        printf("x == y is true\n");
+    } else {
+        printf("x == y is false\n");
+    }
+
+    printf("\nTesting != operator:\n");
+    if (x != y) {
+        printf("x != y is true\n");
+    }
+    if (x != -5) {
+        printf("x != -5 is true\n");
+    } else {
+        printf("x != -5 is false\n");
+    }
+
+    printf("\nTesting while loop with counter:\n");
+    int count = 0;
+    while (count != 5) {
+        printf("count = %d\n", count);
+        count = count + 1;
+    }
+
+    printf("\nTesting while(1) with break condition:\n");
+    int i = 0;
+    while (1) {
+        printf("i = %d\n", i);
+        i = i + 1;
+        if (i == 3) {
+            printf("Breaking out of infinite loop\n");
+            return 0;
+        }
+    }
+
+    return 0;
+}
diff --git a/tests/math_test.rc b/tests/math_test.rc
new file mode 100644
index 0000000..a76bac5
--- /dev/null
+++ b/tests/math_test.rc
@@ -0,0 +1,31 @@
+int main() {
+    printf("Testing Math Functions:\n\n");
+
+    int x = 16;
+    int result = sqrt(x);
+    printf("sqrt(16) = %d\n", result);
+
+    int p = pow(2, 8);
+    printf("pow(2, 8) = %d\n", p);
+
+    int a = abs(-42);
+    printf("abs(-42) = %d\n", a);
+
+    int f = floor(7);
+    printf("floor(7) = %d\n", f);
+
+    int c = ceil(7);
+    printf("ceil(7) = %d\n", c);
+
+    printf("\nTesting with negative numbers:\n");
+    int neg = -100;
+    int abs_neg = abs(neg);
+    printf("abs(-100) = %d\n", abs_neg);
+
+    printf("\nTesting pow with different values:\n");
+    printf("pow(3, 3) = %d\n", pow(3, 3));
+    printf("pow(5, 2) = %d\n", pow(5, 2));
+    printf("pow(10, 3) = %d\n", pow(10, 3));
+
+    return 0;
+}
diff --git a/tests/string_manip_test.rc b/tests/string_manip_test.rc
new file mode 100644
index 0000000..09c407e
--- /dev/null
+++ b/tests/string_manip_test.rc
@@ -0,0 +1,72 @@
+int main() {
+    printf("=== String Manipulation Tests ===\n\n");
+
+    char *text = "Hello World";
+
+    printf("Testing strpos:\n");
+    int pos = strpos(text, "World");
+    printf("Position of 'World' in 'Hello World': %d\n", pos);
+    int pos2 = strpos(text, "xyz");
+    printf("Position of 'xyz' in 'Hello World': %d\n\n", pos2);
+
+    printf("Testing substr:\n");
+    char *sub = substr(text, 0, 5);
+    printf("substr('Hello World', 0, 5) = '%s'\n", sub);
+    char *sub2 = substr(text, 6, 5);
+    printf("substr('Hello World', 6, 5) = '%s'\n\n", sub2);
+
+    printf("Testing upper and lower:\n");
+    char *up = upper(text);
+    printf("upper('Hello World') = '%s'\n", up);
+    char *low = lower(text);
+    printf("lower('Hello World') = '%s'\n\n", low);
+
+    printf("Testing strip:\n");
+    char *spaced = "  Hello World  ";
+    char *stripped = strip(spaced);
+    printf("strip('  Hello World  ') = '%s'\n\n", stripped);
+
+    printf("Testing replace:\n");
+    char *replaced = replace(text, "World", "Python");
+    printf("replace('Hello World', 'World', 'Python') = '%s'\n", replaced);
+    char *replaced2 = replace("aaa bbb aaa", "aaa", "xxx");
+    printf("replace('aaa bbb aaa', 'aaa', 'xxx') = '%s'\n\n", replaced2);
+
+    printf("Testing startswith:\n");
+    if (startswith(text, "Hello")) {
+        printf("'Hello World' starts with 'Hello': true\n");
+    }
+    if (startswith(text, "World")) {
+        printf("'Hello World' starts with 'World': true\n");
+    } else {
+        printf("'Hello World' starts with 'World': false\n");
+    }
+
+    printf("\nTesting endswith:\n");
+    if (endswith(text, "World")) {
+        printf("'Hello World' ends with 'World': true\n");
+    }
+    if (endswith(text, "Hello")) {
+        printf("'Hello World' ends with 'Hello': true\n");
+    } else {
+        printf("'Hello World' ends with 'Hello': false\n");
+    }
+
+    printf("\nTesting slicing [start:end]:\n");
+    char *str = "Python Programming";
+    char *slice1 = str[0:6];
+    printf("'Python Programming'[0:6] = '%s'\n", slice1);
+    char *slice2 = str[7:18];
+    printf("'Python Programming'[7:18] = '%s'\n", slice2);
+    char *slice3 = str[7:11];
+    printf("'Python Programming'[7:11] = '%s'\n", slice3);
+
+    printf("\nCombining operations:\n");
+    char *combined = upper(str[0:6]);
+    printf("upper('Python Programming'[0:6]) = '%s'\n", combined);
+
+    char *chain = replace(lower("HELLO WORLD"), "world", "python");
+    printf("replace(lower('HELLO WORLD'), 'world', 'python') = '%s'\n", chain);
+
+    return 0;
+}
diff --git a/tests/string_test.rc b/tests/string_test.rc
new file mode 100644
index 0000000..4b9c3d5
--- /dev/null
+++ b/tests/string_test.rc
@@ -0,0 +1,29 @@
+int main() {
+    printf("Testing String Concatenation:\n\n");
+
+    char *hello = "Hello";
+    char *world = " World";
+    char *result = hello + world;
+    printf("Result: %s\n", result);
+
+    printf("\nTesting multiple concatenations:\n");
+    char *a = "aaa";
+    char *b = "bbb";
+    char *c = "ccc";
+    char *abc = a + b + c;
+    printf("a + b + c = %s\n", abc);
+
+    printf("\nTesting literal concatenation:\n");
+    char *direct = "First" + " Second" + " Third";
+    printf("Result: %s\n", direct);
+
+    printf("\nTesting with variable and literal:\n");
+    char *name = "Alice";
+    char *greeting = "Hello, " + name + "!";
+    printf("%s\n", greeting);
+
+    printf("\nTesting in printf directly:\n");
+    printf("Direct: %s\n", "Start" + " Middle" + " End");
+
+    return 0;
+}