Click here to download palindromes.c.

/************************************
Write a program that reads in a string
from the user and tells the user whether
or not it is a palindrome.
************************************/
#include <stdio.h>
#include <string.h>

int reverses(char* s1, char* s2);

int main() {
  // Get string from used
  char word[128];
  printf("Enter string: ");
  fflush(stdout);
  scanf(" %s", word);

  // Print whether A and B are reverses
  if (reverses(word, word)) {
    printf("It's a palindrome!\n");
  } else {
    printf("Not a palindrome.\n");
  }

  return 0;
}

// Tests whether s1 and s2 are reverses of one another
int reverses(char* s1, char* s2) {
  // Get lengths and make sure they're equal!
  int len = strlen(s1);
  if (len != strlen(s2)) {
    return 0;
  }

  // test forward on s1 and reverse on s2
  int fwd = 0;
  int rev = len - 1;
  while (rev >= 0) {
    if (s1[fwd] != s2[rev]) {
      return 0;
    }
    ++fwd;
    --rev;
  }

  return 1;
}