C Program to Check String is Palindrome or Not

Check String is Palindrome or Not in C

The question is, write a program in C to enter any string at run-time and check whether it is palindrome or not.

Those string whose all the opposite characters are same is palindrome. And if any of the opposite character mismatched, then the string is not palindrome. For example, codoc is palindrome, codssdoc is palindrome, codes is not palindrome, codescracker is not palindrome.

C Programming Code to Check String is Palindrome or Not

The C program given below asks from the user to enter string at run-time, and checks whether it is a palindrome or not, to display the message at output screen accordingly.

// Write a program in C to input in string
// and check whether it is palindrome or not

#include<stdio.h>
#include<conio.h>
#include<string.h>
int main()
{
	char str[50];
	int i, j, len, chk=0;
	printf("Enter any string (word): ");
	scanf("%s", str);
	len = strlen(str);
	for(i=0, j=(len-1); i<=(len-1); i++, j--)
	{
		if(str[i] != str[j])
		{
			chk=1;
			break;
		}
	}
	if(chk==1)
	{
		printf("The string is Not Palindrome.");
	}
	else
	{
		printf("The string is Palindrome.");
	}
	getch();
	return 0;
}

The above program is written under CodeBlocks IDE and therefore here is the output after build and run. This is the first screenshot of first sample run:

And here is the second screenshot of first sample run:

As the reverse of codescracker is rekcarcsedoc which is not equal to the original string, that is codescracker, therefore the string is not palindrome.

Here is the first screenshot of second sample run:

Here in this case, the reverse of codoc is codoc which is same as the original string, that is codoc, therefore the string is palindrome.

Main Steps Involved in above Program

Here are the steps involved in above program:

• first we have to count the length of string using strlen() function. For example, let's suppose the length of string is 6.
• create a loop to compare first character of the string to the last, and then second to the second last and so on. Therefore here first character is compared to the sixth character, and then second to the fifth, and third to the fourth. As indexing starts from 0, therefore, here we have to minus one from all. That is, 0^{th to the length-1.}
• If any of the above comparision goes wrong, or if any character mismatched, then we have to initialize any number to any character for the checking purpose on later, that whether this loop is run or not (this loop tolds that whether any opposite character mismatched or not), say 1 to chk here in the above example. And then break out of the loop. As if any of the opposite character in the string mismatched, then we have to break out of the loop.
• now after exiting from the loop whether using break statement or after running the whole loop. We have to check whether the variable say chk holds its original value, that is 0 or not. If it holds its original value, then none of the opposite character mismatched (means it is palindrome), and if it doesn't holds its original value, then any of the opposite character mismatched (means it is not palindrome).
• Here mismatched occurs, means the string is not palindrome, otherwise the string is palindrome.

Here is another sample run for palindrome string:

And here is one more sample run for not palindrome string:

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