C Program to Check the Given String is Palindrome

A string can be Palindrome string in C, if it is remained same when we reversed it. In this article, we will show you, How to write a C Program to Check the Given String is Palindrome using Built-in functions, and without using built-in functions.

C Program to Check the Given String is Palindrome Example 1

This program for string palindrome in c allows the user to enter a string (or character array), and a character value. Next, it will check whether the user specified string is a palindrome string or not.

/* C Program to Check the given string is Palindrome or not */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100];
  	int i, len, flag;
  	flag = 0;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	len = strlen(str);
  	 	   	
  	for(i = 0; i < len; i++)
	{
		if(str[i] != str[len - i - 1])
		{
			flag = 1;
			break;	
		} 
	}
	if(flag == 0)
	{
		printf("\n %s is a Palindrome String", str);
	}
	else
	{
		printf("\n %s is Not a Palindrome String", str);
	}	
	
  	return 0;
}

OUTPUT

ANALYSIS
Here, we used For Loop to iterate each and every character in a String, and check the palindrome condition

for(i = 0; i < len; i++)
{
	if(str[i] != str[len - i - 1])
	{
		flag = 1;
		break;	
	} 
}

str[] = wow
len = 3
Flag = 0

For Loop – First Iteration: for(i = 0; i < len ; i++)
The condition is True because 0 < 3.
Within the For Loop we used If Statement to check whether the str[1] is not equal to str[len – i – 1]
if(str[i] != str[len – i – 1]) => if(str[0] != str[3 – 0 – 1])
if(w != w) – Condition is False. So, Flag is still 0

Second Iteration: for(i = 1; 1 < 3 ; 1++)
if(str[i] != str[len – i – 1]) => if(str[1] != str[3 – 1 – 1])
if(o != o) – Condition is False. So, Flag is still 0

Third Iteration: for(i = 2; 2 < 3 ; 2++)
if(str[i] != str[len – i – 1]) => if(str[2] != str[3 – 2 – 1])
if(w != w) – Condition is False. So, Flag is still 0
Next, we used If Else Statement to check the Flag value is 0 or not.

Remember, If condition in any of the loop is True then Flag value will become one, and string will not be palindrome string in C

Let me check another string

C Program to Check the Given String is Palindrome Example 2

This string palindrome in c program is same as above but we changed the logic a bit.

/* C Program to Check the given string is Palindrome or not */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100];
  	int i, len, stratIndex, endIndex;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	len = strlen(str);
  	endIndex = len - 1;
	    	 	   	
  	for(i = 0; i <= endIndex; i++)
	{
		if(str[i] != str[endIndex])
		{
			break;	
		} 
		endIndex--;		
	}
	if(i >= endIndex)
	{
		printf("\n %s is a Palindrome String", str);
	}
	else
	{
		printf("\n %s is Not a Palindrome String", str);
	}	
	
  	return 0;
}

OUTPUT

C Program to Check the Given String is Palindrome Example 3

In this C program for string palindrome, we are using the traditional approach. First, we are reversing the string, and then we are comparing reversed string with original string. I suggest you to refer Reverse a String article to understand the steps involved in string reverse.

/* C Program to Check the given string is Palindrome or not */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100], revstr[100];
  	int i, j, len, flag;
  	flag = 0;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	len = strlen(str);
  	j = 0;

  	// Reverse a String 	   	
  	for(i = len - 1; i >= 0; i--)
	{
		revstr[j++] = str[i];
	}
	revstr[i] = '\0';

	// Comparing Reverse String and Original String
	for(i = 0; i < len; i++)
	{
		if(str[i] != revstr[i])
		{
			flag = 1;
			break;	
		} 
	}
	if(flag == 0)
	{
		printf("\n %s is a Palindrome String", str);
	}
	else
	{
		printf("\n %s is Not a Palindrome String", str);
	}	
	
  	return 0;
}

OUTPUT

C Program to Check the Given String is Palindrome Example 4

This program for string palindrome in c is same as second example but this time we are using the Functions concept to separate the logic.

/* C Program to Check the given string is Palindrome or not */
 
#include <stdio.h>
#include <string.h>

void isPalindrome(char str[]);
 
int main()
{
  	char str[100];
 
  	printf("\n Please Enter any String :  ");
  	gets(str);
  	
  	isPalindrome(str);	
	
  	return 0;
}

void isPalindrome(char str[])
{
	int i = 0;
	int len = strlen(str) - 1;
	
	while (len > i)
	{
		if(str[i++] != str[len--])
		{
			printf("\n %s is Not a Palindrome String", str);
			return;
		}
	}
	printf("\n %s is a Palindrome String", str);
}

OUTPUT

C Program to Check the Given String is Palindrome using  Built-in Functions

In this string palindrome in c program we are using the built-in functions strcpy, strrev, and strcmp.

First, strcpy to copy the user given string to new string. Next, we used the strive to reverse the string. And finally, we used strcmp to compare the original string with reverse one.

/* C Program to Check the given string is Palindrome or not */
 
#include <stdio.h>
#include <string.h>
 
int main()
{
  	char str[100], revstr[100];
  	int flag;
 
  	printf("\n Please Enter any String :  ");
  	gets(str);

  	// To Copy the string to revstr
  	strcpy(revstr, str);

  	strrev(revstr); // reverse the string

  	// Comparing string
	flag = strcmp(str, revstr); 

	if(flag == 0)
	{
		printf("\n %s is a Palindrome String", str);
	}
	else
	{
		printf("\n %s is Not a Palindrome String", str);
	}	
	
  	return 0;
}

OUTPUT

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