Debug smarter.
Learn faster.

#include <stdio.h>

void reverse(char *str) {
    int len = strlen(str);
    // 🤔 something's off here...
    for (int i = 0; i <= len; i++) {
        char tmp = str[i];
        str[i] = str[len - i];
        str[len - i] = tmp;
    }
}

// → get a hint ↓