# RC Programming Language Tutorial

Complete guide to the RC (Retoor's C) programming language - a C-like interpreted language with enhanced string manipulation capabilities.

## Table of Contents

1. [Basic Program Structure](#basic-program-structure)
2. [Data Types](#data-types)
3. [Variables and Declarations](#variables-and-declarations)
4. [Arrays](#arrays)
5. [Operators](#operators)
    - [Arithmetic Operators](#arithmetic-operators)
    - [Comparison Operators](#comparison-operators)
    - [Logical Operators](#logical-operators)
    - [Unary Operators](#unary-operators)
    - [Increment and Decrement Operators](#increment-and-decrement-operators)
6. [Control Flow](#control-flow)
7. [Functions](#functions)
8. [Pointers](#pointers)
9. [Output with printf](#output-with-printf)
10. [String Operations](#string-operations)
11. [String Slicing](#string-slicing)
12. [Math Functions](#math-functions)
13. [String Manipulation Functions](#string-manipulation-functions)
14. [Socket Programming](#socket-programming)
15. [Comments](#comments)

---

## Basic Program Structure

Every RC program must have a `main` function that returns an integer.

```c
int main() {
    printf("Hello, World!\n");
    return 0;
}
```

## Data Types

RC supports two primary data types:

### Integer (int)

```c
int x = 42;
int y = -10;
int z;  // Uninitialized variable
```

### Character Pointer (char*)

Used for strings.

```c
char *name = "Alice";
char *message = "Hello, World!";
char *empty = "";
```

## Variables and Declarations

### Variable Declaration

```c
int main() {
    int age = 25;
    int count;
    count = 10;

    char *name = "Bob";
    char *greeting;
    greeting = "Hi there!";

    return 0;
}
```

### Multiple Variables

```c
int main() {
    int a = 1, b = 2, c = 3;
    char *first = "Hello", *second = "World";

    printf("a=%d, b=%d, c=%d\n", a, b, c);
    return 0;
}
```

## Arrays

### Integer Arrays

```c
int main() {
    int numbers[5];
    numbers[0] = 10;
    numbers[1] = 20;
    numbers[2] = 30;

    printf("First: %d\n", numbers[0]);
    printf("Second: %d\n", numbers[1]);

    return 0;
}
```

### Character Arrays (Buffers)

```c
int main() {
    char buffer[100];
    int i = 0;

    buffer[0] = 65;  // ASCII 'A'
    buffer[1] = 66;  // ASCII 'B'
    buffer[2] = 0;   // Null terminator

    return 0;
}
```

## Operators

### Arithmetic Operators

```c
int main() {
    int a = 10;
    int b = 3;

    printf("Addition: %d\n", a + b);      // 13
    printf("Subtraction: %d\n", a - b);   // 7
    printf("Multiplication: %d\n", a * b); // 30
    printf("Division: %d\n", a / b);      // 3

    return 0;
}
```

### Comparison Operators

```c
int main() {
    int x = 5;
    int y = 10;

    if (x == y) printf("Equal\n");
    if (x != y) printf("Not equal\n");
    if (x < y) printf("Less than\n");
    if (x > y) printf("Greater than\n");
    if (x <= y) printf("Less or equal\n");
    if (x >= y) printf("Greater or equal\n");

    return 0;
}
```

### Logical Operators

```c
int main() {
    int a = 1;
    int b = 0;

    if (a && b) printf("Both true\n");
    if (a || b) printf("At least one true\n");

    return 0;
}
```

### Unary Operators

```c
int main() {
    int x = 10;
    int y = -x;  // Negation

    printf("x = %d\n", x);   // 10
    printf("y = %d\n", y);   // -10

    return 0;
}
```

### Increment and Decrement Operators

RC supports both pre-increment/decrement (`++x`, `--x`) and post-increment/decrement (`x++`, `x--`) operators.

#### Post-increment (`x++`)
The value of the expression is the value of `x` *before* the increment.
```c
int main() {
    int x = 5;
    int y = x++; // y is 5, x becomes 6
    printf("x = %d, y = %d\n", x, y);
    return 0;
}
```

#### Pre-increment (`++x`)
The value of the expression is the value of `x` *after* the increment.
```c
int main() {
    int x = 5;
    int y = ++x; // y is 6, x becomes 6
    printf("x = %d, y = %d\n", x, y);
    return 0;
}
```

#### Post-decrement (`x--`)
The value of the expression is the value of `x` *before* the decrement.
```c
int main() {
    int x = 5;
    int y = x--; // y is 5, x becomes 4
    printf("x = %d, y = %d\n", x, y);
    return 0;
}
```

#### Pre-decrement (`--x`)
The value of the expression is the value of `x` *after* the decrement.
```c
int main() {
    int x = 5;
    int y = --x; // y is 4, x becomes 4
    printf("x = %d, y = %d\n", x, y);
    return 0;
}
```

## Control Flow

### If-Else Statements

```c
int main() {
    int age = 18;

    if (age >= 18) {
        printf("Adult\n");
    } else {
        printf("Minor\n");
    }

    return 0;
}
```

### Nested If-Else

```c
int main() {
    int score = 85;

    if (score >= 90) {
        printf("Grade: A\n");
    } else if (score >= 80) {
        printf("Grade: B\n");
    } else if (score >= 70) {
        printf("Grade: C\n");
    } else {
        printf("Grade: F\n");
    }

    return 0;
}
```

### While Loops

```c
int main() {
    int i = 0;

    while (i < 5) {
        printf("Count: %d\n", i);
        i = i + 1;
    }

    return 0;
}
```

### Infinite Loops with Break Condition

```c
int main() {
    int counter = 0;

    while (1) {
        printf("Iteration: %d\n", counter);
        counter = counter + 1;

        if (counter == 10) {
            printf("Breaking loop\n");
            return 0;
        }
    }

    return 0;
}
```

## Functions

### Function Definition

```c
int add(int a, int b) {
    return a + b;
}

int main() {
    int result = add(5, 3);
    printf("Result: %d\n", result);
    return 0;
}
```

### Function with No Parameters

```c
int get_constant() {
    return 42;
}

int main() {
    int value = get_constant();
    printf("Value: %d\n", value);
    return 0;
}
```

### Recursive Functions

```c
int factorial(int n) {
    if (n <= 1) {
        return 1;
    }
    return n * factorial(n - 1);
}

int main() {
    printf("5! = %d\n", factorial(5));  // 120
    return 0;
}
```

### Functions Returning Strings

```c
char *get_greeting() {
    return "Hello, RC!";
}

int main() {
    char *message = get_greeting();
    printf("%s\n", message);
    return 0;
}
```

## Pointers

### Address-of Operator (&)

```c
int main() {
    int x = 42;
    int addr = &x;  // Get address of x

    printf("Value: %d\n", x);
    printf("Address: %d\n", addr);

    return 0;
}
```

### Dereference Operator (*)

```c
int main() {
    int x = 42;
    int addr = &x;
    int value = *addr;  // Dereference to get value

    printf("Original: %d\n", x);
    printf("Via pointer: %d\n", value);

    return 0;
}
```

### Pointer Assignment

```c
int main() {
    int x = 10;
    int addr = &x;

    *addr = 20;  // Modify x through pointer

    printf("x is now: %d\n", x);  // 20

    return 0;
}
```

## Output with printf

### Basic Printf

```c
int main() {
    printf("Hello, World!\n");
    return 0;
}
```

### Printing Integers

```c
int main() {
    int age = 25;
    printf("Age: %d\n", age);
    printf("Multiple: %d and %d\n", 10, 20);
    return 0;
}
```

### Printing Strings

```c
int main() {
    char *name = "Alice";
    printf("Name: %s\n", name);
    printf("Greeting: %s %s\n", "Hello", name);
    return 0;
}
```

### Escape Sequences

```c
int main() {
    printf("Line 1\nLine 2\n");  // Newline
    printf("Tab\there\n");        // Note: Only \n is supported
    return 0;
}
```

## String Operations

### String Concatenation with +

```c
int main() {
    char *first = "Hello";
    char *second = " World";
    char *result = first + second;

    printf("%s\n", result);  // "Hello World"

    return 0;
}
```

### Multiple Concatenation

```c
int main() {
    char *a = "RC ";
    char *b = "is ";
    char *c = "awesome!";
    char *message = a + b + c;

    printf("%s\n", message);  // "RC is awesome!"

    return 0;
}
```

### Concatenation with Literals

```c
int main() {
    char *name = "Alice";
    char *greeting = "Hello, " + name + "!";

    printf("%s\n", greeting);  // "Hello, Alice!"

    return 0;
}
```

## String Slicing

### Basic Slicing [start:end]

```c
int main() {
    char *text = "Hello World";

    char *first_word = text[0:5];
    char *second_word = text[6:11];

    printf("First: %s\n", first_word);   // "Hello"
    printf("Second: %s\n", second_word);  // "World"

    return 0;
}
```

### Slicing Examples

```c
int main() {
    char *str = "Programming";

    printf("First 4: %s\n", str[0:4]);      // "Prog"
    printf("Middle: %s\n", str[3:7]);       // "gram"
    printf("Last 4: %s\n", str[7:11]);      // "ming"

    return 0;
}
```

### Combining Slicing with Operations

```c
int main() {
    char *text = "hello world";

    char *uppercase = upper(text[0:5]);
    printf("%s\n", uppercase);  // "HELLO"

    char *combined = text[0:5] + " " + text[6:11];
    printf("%s\n", combined);  // "hello world"

    return 0;
}
```

## Math Functions

All math functions return integers (long). Floating-point values are truncated.

### sqrt(x) - Square Root

```c
int main() {
    printf("sqrt(16) = %d\n", sqrt(16));    // 4
    printf("sqrt(25) = %d\n", sqrt(25));    // 5
    printf("sqrt(100) = %d\n", sqrt(100));  // 10
    return 0;
}
```

### pow(base, exp) - Power

```c
int main() {
    printf("2^3 = %d\n", pow(2, 3));     // 8
    printf("10^2 = %d\n", pow(10, 2));   // 100
    printf("5^4 = %d\n", pow(5, 4));     // 625
    return 0;
}
```

### abs(x) - Absolute Value

```c
int main() {
    printf("abs(-42) = %d\n", abs(-42));   // 42
    printf("abs(42) = %d\n", abs(42));     // 42
    printf("abs(0) = %d\n", abs(0));       // 0
    return 0;
}
```

### Trigonometric Functions

Note: Results are scaled by 1,000,000 for precision.

```c
int main() {
    int s = sin(0);
    int c = cos(0);
    int t = tan(0);

    printf("sin(0) = %d\n", s);
    printf("cos(0) = %d\n", c);
    printf("tan(0) = %d\n", t);

    return 0;
}
```

### floor(x) and ceil(x)

```c
int main() {
    printf("floor(7) = %d\n", floor(7));    // 7
    printf("ceil(7) = %d\n", ceil(7));      // 7

    return 0;
}
```

## String Manipulation Functions

### strpos(haystack, needle) - Find Substring

```c
int main() {
    char *text = "Hello World";

    int pos1 = strpos(text, "World");
    printf("Position of 'World': %d\n", pos1);  // 6

    int pos2 = strpos(text, "xyz");
    printf("Position of 'xyz': %d\n", pos2);    // -1 (not found)

    return 0;
}
```

### substr(str, start, length) - Extract Substring

```c
int main() {
    char *text = "Programming";

    char *sub1 = substr(text, 0, 4);
    printf("substr(0, 4): %s\n", sub1);  // "Prog"

    char *sub2 = substr(text, 3, 4);
    printf("substr(3, 4): %s\n", sub2);  // "gram"

    return 0;
}
```

### upper(str) - Convert to Uppercase

```c
int main() {
    char *text = "hello world";
    char *upper_text = upper(text);

    printf("Original: %s\n", text);        // "hello world"
    printf("Uppercase: %s\n", upper_text); // "HELLO WORLD"

    return 0;
}
```

### lower(str) - Convert to Lowercase

```c
int main() {
    char *text = "HELLO WORLD";
    char *lower_text = lower(text);

    printf("Original: %s\n", text);        // "HELLO WORLD"
    printf("Lowercase: %s\n", lower_text); // "hello world"

    return 0;
}
```

### strip(str) - Remove Leading/Trailing Whitespace

```c
int main() {
    char *text = "  Hello World  ";
    char *stripped = strip(text);

    printf("Original: '%s'\n", text);     // "  Hello World  "
    printf("Stripped: '%s'\n", stripped);  // "Hello World"

    return 0;
}
```

### replace(str, old, new) - Replace Substring

```c
int main() {
    char *text = "Hello World";
    char *replaced = replace(text, "World", "RC");

    printf("Original: %s\n", text);      // "Hello World"
    printf("Replaced: %s\n", replaced);   // "Hello RC"

    return 0;
}
```

### Multiple Replacements

```c
int main() {
    char *text = "foo bar foo";
    char *replaced = replace(text, "foo", "baz");

    printf("%s\n", replaced);  // "baz bar baz"

    return 0;
}
```

### startswith(str, prefix) - Check Prefix

```c
int main() {
    char *text = "Hello World";

    if (startswith(text, "Hello")) {
        printf("Starts with 'Hello'\n");
    }

    if (startswith(text, "World")) {
        printf("Starts with 'World'\n");
    } else {
        printf("Does not start with 'World'\n");
    }

    return 0;
}
```

### endswith(str, suffix) - Check Suffix

```c
int main() {
    char *text = "Hello World";

    if (endswith(text, "World")) {
        printf("Ends with 'World'\n");
    }

    if (endswith(text, "Hello")) {
        printf("Ends with 'Hello'\n");
    } else {
        printf("Does not end with 'Hello'\n");
    }

    return 0;
}
```

### strlen(str) - Get String Length

```c
int main() {
    char *text = "Hello";
    int len = strlen(text);

    printf("Length of '%s': %d\n", text, len);  // 5

    return 0;
}
```

### Combining String Functions

```c
int main() {
    char *text = "  HELLO world  ";

    char *processed = upper(strip(text));
    printf("Result: %s\n", processed);  // "HELLO WORLD"

    char *text2 = "hello";
    char *result = replace(upper(text2), "HELLO", "GOODBYE");
    printf("Result: %s\n", result);  // "GOODBYE"

    return 0;
}
```

## Socket Programming

RC provides native socket functions for network programming.

### Basic HTTP Server

```c
int main() {
    int sockfd;
    int client_fd;
    char buffer[1024];

    sockfd = socket(AF_INET(), SOCK_STREAM(), 0);
    bind(sockfd, 8080);
    listen(sockfd, 10);

    printf("Server listening on port 8080\n");

    client_fd = accept(sockfd, 0, 0);
    printf("Client connected\n");

    recv(client_fd, buffer, 1024, 0);

    send(client_fd, "HTTP/1.1 200 OK\n\nHello!\n", 24, 0);

    close(client_fd);
    close(sockfd);

    return 0;
}
```

### Socket Functions

**socket(domain, type, protocol)** - Create socket
```c
int sockfd = socket(AF_INET(), SOCK_STREAM(), 0);
```

**bind(sockfd, port)** - Bind socket to port
```c
bind(sockfd, 8080);
```

**listen(sockfd, backlog)** - Listen for connections
```c
listen(sockfd, 10);
```

**accept(sockfd, addr, addrlen)** - Accept connection
```c
int client = accept(sockfd, 0, 0);
```

**recv(sockfd, buffer, length, flags)** - Receive data
```c
int bytes = recv(client, buffer, 1024, 0);
```

**send(sockfd, data, length, flags)** - Send data
```c
send(client, "Hello", 5, 0);
```

**close(fd)** - Close socket
```c
close(sockfd);
```

**Constants:**
- `AF_INET()` - IPv4 address family
- `SOCK_STREAM()` - TCP socket type

## Comments

RC supports single-line comments using `//`.

```c
int main() {
    // This is a comment
    int x = 10;  // Inline comment

    // Multiple lines of comments
    // can be written like this
    printf("Hello\n");

    return 0;
}
```

---

## Complete Examples

### Example 1: Text Processing

```c
int main() {
    char *text = "  hello WORLD  ";

    char *cleaned = strip(text);
    char *lowercase = lower(cleaned);
    char *replaced = replace(lowercase, "world", "rc");
    char *final = upper(replaced);

    printf("Original: '%s'\n", text);
    printf("Final: '%s'\n", final);

    return 0;
}
```

### Example 2: String Analysis

```c
int main() {
    char *email = "user@example.com";

    int at_pos = strpos(email, "@");
    int dot_pos = strpos(email, ".");

    if (at_pos > 0 && dot_pos > at_pos) {
        printf("Valid email format\n");

        char *username = substr(email, 0, at_pos);
        printf("Username: %s\n", username);
    }

    return 0;
}
```

### Example 3: Loop with Conditions

```c
int main() {
    int i = 0;

    while (i < 10) {
        if (i == 5) {
            printf("Halfway!\n");
        }

        printf("Count: %d\n", i);
        i = i + 1;
    }

    printf("Done!\n");
    return 0;
}
```

### Example 4: Recursive Fibonacci

```c
int fibonacci(int n) {
    if (n <= 1) {
        return n;
    }
    return fibonacci(n - 1) + fibonacci(n - 2);
}

int main() {
    int i = 0;
    while (i < 10) {
        printf("fib(%d) = %d\n", i, fibonacci(i));
        i = i + 1;
    }
    return 0;
}
```

---

## Best Practices

1. **Always initialize variables** before use
2. **Use meaningful variable names** for readability
3. **Check string operation results** for edge cases
4. **Close sockets** after use in network programming
5. **Return 0** from main to indicate success
6. **Use comments** to explain complex logic
7. **Test edge cases** like empty strings and zero values
8. **Validate user input** in interactive programs

## Limitations

- No floating-point arithmetic (use integers)
- No structs, unions, or custom types
- No preprocessor directives
- Only `\n` escape sequence supported
- Limited to basic C subset
- No file I/O (except socket I/O)
- Memory is managed automatically

---

For more examples, see the `tests/` and `examples/` directories in the RC repository.