Friday, April 22, 2011

Checking if String is Palindrome in C

Palindrome String : are those string which is same if you read it backwards."MADAM" or "AABBCCCCBBAA" are palindrome but "TATA" is not. Its a good practice for starters to check their recursion knowledge with this kind of problem. As we know this can be implemented in recursive way too. but a non recursive way will always compare the first letter of the string to the last letter.
Method : checking if string is palindrome in C can be done by creating a function. The Function checkPalindromeStr uses 2 char pointers start and end . Assign first pointer to start char and other to last char. Then we start matching start pointer to end pointer, when they don't match the given string cant be palindrome so we return 0. else we continue by increasing start and decreasing end  till start crosses end pointer. At that point the string will be palindrome and we return 1.

Code:


#include<stdio.h>
#include<string.h>//for strlen function
int checkPalindromeStr(char* p)
{
    int l;
    char* start;//to denote starting char of string
    char* end;// to denote end of string
    l=strlen(p);    //get length of string;
    start=p;//set start to first char of string
    end=p+l-1;//move end pointer to end char of string
    while(start<=end)
    {
        if(*start==*end)
        {
            start++;
            end--;
        }
        else
        {
            return(0);//string is not palindrome
        }
    }
    return(1);
}
void main()
{
    char* s="aabaa";
    if(checkPalindromeStr(s))
    {
        printf("\n String is Palindrome\n");
    }
    else
    {
        printf("\n String is not Palindrome\n");
    }
}
the same problem can be done using recursion.Follow my this post.
http://programs-in-c-plus-plus.blogspot.com/2011/04/checking-if-string-is-palindrome-in-c_22.html

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