Program to Check Palindrome String in C, Python

In this program, we check how to write the code to identify if the given string is palindrome or not. Before writing a program for palindrome you should know what is palindrome string.

What is Palindrome String?

The string is called a palindrome string if it is read the same forward and backward. In other words, if we reverse the string, it should be identical to the original string.

Palindrome String Example:

String “madam” and “radar” are palindrome strings.

Algorithm to Check Palindrome String

Consider you have given a string.

Algorithm:

Step 1: 
Set the two pointers: 
 - pointer pointing to first (forward Pointer) and 
 - pointer pointing to last character (backword pointer).

Step2: 
 Match the characters pointed by both pointers.

Step 3: 
 If matches, move forward pointer by one to right and move the backward pointer by one to left. And repeat the step 2.
 If don't match, print output as "String is not palindrome"

Difficulty level: low

C Program for Palindrome

We can do this programmatically in the easiest way. Use the string function strrev() provided in string.h library. It reverses the given string. By matching an original string with a reversed string, we can find out if the string is palindrome or not.

Here is a simple C program for palindrome.

#include <stdio.h>
#include <string.h>
  
int main()
{
   char sString[100] = {0};
  
   printf("Enter the string to check if it is a palindrome\n");
   gets(sString);
 
   if (strcmp(sString, strrev((char*)sString)) == 0)
      printf("Given String is a palindrome.\n");
   else
      printf("Given String is not a palindrome.\n");
  
   return 0;
}

Output:

Case 1:

Enter the string to check if it is a palindrome
"radar"
Given String is a palindrome.

Case 2:

Enter the string to check if it is a palindrome
"csestack"
Given String is not a palindrome.

Note:

On some systems, you may come across an error as “Undefined reference to strrev“. This is all because strrev() is not supports in the C-GCC compiler. It is present in ANSI C (Turbo C/C++) compilers.

In the case of the C-GCC compiler, you have to write code to reverse the string manually and then have to match the string.

Python Program for Palindrome

Here is simple program in Python to check if the given string is palindrome or not.

str_msg = "radar"

if str_msg == str_msg[::-1]:
  print(f"{str_msg} is a palindrome string.")
else:
  print(f"{str_msg} is not a palindrome string.")

Output:

radar is a palindrome string.

Here, we are using extended slice syntax for reversing the string.

You can try executing the above Python code for different string.

Complexity

Considering the number of characters in the string as n, reversing and comparing would take O(n) time each. This leads to the total complexity of O(n).

[Complexity of the program has updated as per the correction by Amey in the comment. Thanks, Amey!]

Aniruddha Chaudhari

I am a Python enthusiast who loves Linux and Vim. I hold a Master of Computer Science degree from NIT Trichy and have 10 years of experience in the IT industry, focusing on the Software Development Lifecycle from Requirements Gathering, Design, Development to Deployment. I have worked at IBM, Ericsson, and NetApp, and I share my knowledge on CSEstack.org.