to find if a given string is palindrome or is not palindrome

Question

I made a program to find if a entered string is palindrome or not palindrome but it always says that its not a palindrome

#include  
#include          


        

Answer 1

To give you a clue I've done some tidier indenting of a bit of your code:

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

Answer 2

A C-flavored solution : )

bool is_palindrome(const char* s) {
    const char* p = s;
    while (*p != '\0') ++p;
    while (s < p) if (*s++ != *--p) return false;
    return true;
}

Answer 3

bool isPalindrome(char* str) {
    char* s = str;
    char* e = str;
    while(*e) e++;
    --e;
    while(s < e) {
        if(*s != *e) return false;
        ++s; --e;
    }
    return true;
}

Answer 4

Here you want something like...

    if(str[i]!=str[strlen (str) - i - 1])
    {
        flag = 0;
        break;
    }

The break needs to go in the if block otherwise it will always get executed. Initialising flag at some point would be a good idea, too. If I might be permitted an observation, ALWAYS enclose the if-block and else block in curly brackets even if there is only one statement; it would save you several of the problems you've got here.

Later - edited per Mr Rodriguez' comments below.

Answer 5

Here is a better way.

#include <iostream>
#include <algorithm>
#include <string>
using namespace std;
int main() {
    string input;
    cout << "Enter your text: ";
    cin >> input;
    transform(input.begin(), input.end(), input.begin(), ::tolower);
    if (input[0] == input[input.length()-1])
        cout << "Palindrome";
    else
        cout << "not palinrome";
    cin.ignore();
    cin.get();
}

Answer 6

From the 2005 version of myself:

bool isAlphaNumeric(char c)
{
    return (iswalpha(c) || iswdigit(c));
}

bool isPalindrome(char *str)
{
    /* A man, a plan, Anal Panama!!! */
    if(*str == '\0')
    {
        return false;
    }

    int len = strlen(str);
    if(len <= 1) return true;

    char *start = str;
    char *end = start + len - 1;

    while(start < end)
    {
        if(!isAlphaNumeric(*start))
        {
            *start++;
            continue;
        }
        if(!isAlphaNumeric(*end))
        {
            *end--;
            continue;
        }
        if(towlower(*start) != towlower(*end))
        {
            return false;
        }
        *start++;
        *end--;
    }
    return true;
}