Implement mystrlen and mystr_idx functions

munit/str_lib.c

@@ -0,0 +1,33 @@
+#include "str_lib.h"
+
+size_t mystrlen(const char *str) {
+    if (!str) return 0;
+    size_t len = 0;
+    while (str[len] != '\0') {
+        len++;
+    }
+    return len;
+}
+
+int mystr_idx(const char *str, const char *substr) {
+    if (!str || !substr) return -1;
+    
+    size_t str_len = mystrlen(str);
+    size_t substr_len = mystrlen(substr);
+    
+    if (substr_len == 0) return 0;
+    if (substr_len > str_len) return -1;
+    
+    for (size_t i = 0; i <= str_len - substr_len; i++) {
+        int found = 1;
+        for (size_t j = 0; j < substr_len; j++) {
+            if (str[i + j] != substr[j]) {
+                found = 0;
+                break;
+            }
+        }
+        if (found) return i;
+    }
+    
+    return -1;
+}