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Palindrome in C

C program to check if a string or a number is palindrome or not. A palindrome string is one that reads the same backward as well as forward. It can be of odd or even length. A palindrome number is a number that is equal to its reverse. Our program works as follows: at first, we copy input string into a new string (strcpy function), and then we reverse (strrev function) it and compare it with the original string (strcmp function). If both of them have the same sequence of characters, i.e., they are identical, then the string is a palindrome otherwise not. C program to check palindrome without using string functions. Some palindrome strings are: "C", "CC", "madam", "ab121ba", "C++&&++C".

Palindrome program in C language

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

int main()
{
  char a[100], b[100];

  printf("Enter a string to check if it's a palindrome\n");
  gets(a);

  strcpy(b, a);  // Copying input string
  strrev(b);  // Reversing the string

  if (strcmp(a, b) == 0)  // Comparing input string with the reverse string
    printf("The string is a palindrome.\n");
  else
    printf("The string isn't a palindrome.\n");

  return 0;
}

Output of C palindrome program:
Palindrome program in C output

Download palindrome program.

C program for palindrome without using string functions

#include <stdio.h>

int main()
{
  char text[100];
  int begin, middle, end, length = 0;

  gets(text);

  while (text[length] != '\0')
    length++;

  end = length - 1;
  middle = length/2;

  for (begin = 0; begin < middle; begin++)
  {
    if (text[begin] != text[end])
    {
      printf("Not a palindrome.\n");
      break;
    }
    end--;
  }
  if (begin == middle)
    printf("Palindrome.\n");

  return 0;
}

Palindrome number in C

#include <stdio.h>

int main()
{
   int n, r = 0, t;

   printf("Enter an integer to check if it's palindrome or not\n");
   scanf("%d", &n);

   t = n;

   while (t != 0)
   {
      r = r * 10;
      r = r + t%10;
      t = t/10;
   }

   if (n == r)
      printf("%d is a palindrome number.\n", n);
   else
      printf("%d isn't a palindrome number.\n", n);

   return 0;
}

C palindrome program using functions and pointers

#include <stdio.h>
 
int is_palindrome(char*);
void copy_string(char*, char*);
void reverse_string(char*);
int string_length(char*);
int compare_string(char*, char*);
 
int main()
{
   char string[100];
   int result;
 
   printf("Input a string\n");
   gets(string);
 
   result = is_palindrome(string);
 
   if (result == 1)
      printf("\"%s\" is a palindrome string.\n", string);
   else
      printf("\"%s\" isn't a palindrome string.\n", string);
 
   return 0;
}
 
int is_palindrome(char *string)
{
   int check, length;
   char *reverse;
 
   length = string_length(string);    
   reverse = (char*)malloc(length+1);    
 
   copy_string(reverse, string);
   reverse_string(reverse);
 
   check = compare_string(string, reverse);
 
   free(reverse);
 
   if (check == 0)
      return 1;
   else
      return 0;
}
 
int string_length(char *string)
{
   int length = 0;  
 
   while(*string)
   {
      length++;
      string++;
   }
 
   return length;
}
 
void copy_string(char *target, char *source)
{
   while(*source)
   {
      *target = *source;
      source++;
      target++;
   }
   *target = '\0';
}
 
void reverse_string(char *string)
{
   int length, c;
   char *begin, *end, temp;
 
   length = string_length(string);
 
   begin = string;
   end = string;
 
   for (c = 0; c < (length - 1); c++)
       end++;
 
   for (c = 0; c < length/2; c++)
   {        
      temp = *end;
      *end = *begin;
      *begin = temp;
 
      begin++;
      end--;
   }
}
 
int compare_string(char *first, char *second)
{
   while(*first==*second)
   {
      if (*first == '\0' || *second == '\0')
         break;
 
      first++;
      second++;
   }
   if (*first == '\0' && *second == '\0')
      return 0;
   else
      return -1;
}

You can also write the program without using pointers. A palindrome string can be a single word or a phrase or a sentence.

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