int main() {
    printf("Testing Edge Cases:\n\n");

    printf("1. Empty string operations:\n");
    char *empty = "";
    char *result1 = upper(empty);
    printf("upper('') = '%s'\n", result1);

    printf("\n2. String slicing edge cases:\n");
    char *text = "Hello";
    char *slice1 = text[0:0];
    printf("'Hello'[0:0] = '%s'\n", slice1);
    char *slice2 = text[10:20];
    printf("'Hello'[10:20] = '%s'\n", slice2);
    char *slice3 = text[3:3];
    printf("'Hello'[3:3] = '%s'\n", slice3);

    printf("\n3. Math with edge cases:\n");
    int zero = 0;
    printf("abs(0) = %d\n", abs(zero));
    printf("sqrt(0) = %d\n", sqrt(zero));

    printf("\n4. String concatenation:\n");
    char *str1 = "A";
    char *str2 = "B";
    char *concat = str1 + str2;
    printf("'A' + 'B' = '%s'\n", concat);

    printf("\n5. String search edge cases:\n");
    int pos1 = strpos("test", "xyz");
    printf("strpos('test', 'xyz') = %d\n", pos1);
    int pos2 = strpos("test", "test");
    printf("strpos('test', 'test') = %d\n", pos2);

    printf("\n6. Nested operations:\n");
    char *nested = upper(lower(upper("TeSt")));
    printf("upper(lower(upper('TeSt'))) = '%s'\n", nested);

    printf("\nAll edge cases handled safely!\n");
    return 0;
}