Reversing a String and Checking for Palindromes

This lesson covers checking whether a string is a palindrome in C, so you understand the basics of string manipulation. It's for anyone searching "C palindrome check implementation."

A string that reads the same forward and backward is called a palindrome. C has no dedicated function for reversing a string, so comparing from both ends toward the middle, one character at a time, is a common approach.

The example's isPalindrome() function compares s[i] (from the front) against s[len - 1 - i] (from the back), looping toward the middle of the string. Notice it returns immediately, deciding it's not a palindrome, the moment even one character differs.

A common early mistake is not thinking of comparing directly from both ends, instead of actually reversing the string. Getting used to this memory-saving idea — comparing purely through index math, without building a new reversed string — takes some practice.

String reversal and palindrome checks don't come up too often in real work, but it's a classic exercise for practicing how to think about string manipulation in general.

📖 Reference code

#include <stdio.h>
#include <string.h>

int isPalindrome(const char *s) {
    int len = strlen(s);
    for (int i = 0; i < len / 2; i++) {
        if (s[i] != s[len - 1 - i]) return 0;
    }
    return 1;
}

int main(void) {
    printf("%d\n", isPalindrome("racecar"));
    printf("%d\n", isPalindrome("hello"));
    return 0;
}

✍️ Your code

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🧪 This site can't compile or run C directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).