String Utilities

#ifndef STRING_UTILS_H#define STRING_UTILS_H#include <stdlib.h>#include <string.h>#include <ctype.h>char* trim(char* str) {    if (str == NULL) return NULL;        // Trim leading whitespace    while (isspace((unsigned char)*str)) str++;        if (*str == 0) return str;        // Trim trailing whitespace    char* end = str + strlen(str) - 1;    while (end > str && isspace((unsigned char)*end)) end--;        end[1] = '\0';    return str;}char* str_replace(const char* str, const char* old, const char* new_str) {    if (str == NULL || old == NULL || new_str == NULL) return NULL;        size_t old_len = strlen(old);    size_t new_len = strlen(new_str);    size_t str_len = strlen(str);        // Count occurrences    int count = 0;    const char* pos = str;    while ((pos = strstr(pos, old)) != NULL) {        count++;        pos += old_len;    }        // Allocate result    size_t result_len = str_len + count * (new_len - old_len);    char* result = (char*)malloc(result_len + 1);    if (result == NULL) return NULL;        // Replace    char* dest = result;    const char* src = str;    while (*src) {        if (strncmp(src, old, old_len) == 0) {            memcpy(dest, new_str, new_len);            dest += new_len;            src += old_len;        } else {            *dest++ = *src++;        }    }    *dest = '\0';        return result;}void to_lowercase(char* str) {    if (str == NULL) return;    for (int i = 0; str[i]; i++) {        str[i] = tolower((unsigned char)str[i]);    }}void to_uppercase(char* str) {    if (str == NULL) return;    for (int i = 0; str[i]; i++) {        str[i] = toupper((unsigned char)str[i]);    }}#endif

#include "string_utils.h"#include <stdio.h>int main() {    char str1[] = "    Hello World    ";    printf("Original: '%s'\n", str1);    printf("Trimmed: '%s'\n", trim(str1));        const char* original = "Hello World";    char* replaced = str_replace(original, "World", "Universe");    if (replaced) {        printf("Replaced: %s\n", replaced);        free(replaced);    }        char str2[] = "Hello World";    to_lowercase(str2);    printf("Lowercase: %s\n", str2);        return 0;}