Check if string is palindrome

Examples of Palindrome string are madam, malayalam, level, refer, radar etc.
Method 1
This method reads a string from the keyboard and then iterates over it using a for loop.
In every iteration, it compares the characters at the left position with the character at corresponding right position.

#include <iostream>
#include <cstring>

using namespace std;

int main()
{
    // variable to hold the string
    string s = "";
    // declare a variable for checking result later
    bool isPalindrome = true;
    cout << "Enter a string" << endl; 
    // read the string
    getline(cin, s);
    // get length of string
    int length = s.length();
    // loop over string
    for(int i = 0; i < length; i++){
        // compare characters from start and end
        if(s[i] != s[length - i - 1]) {
            isPalindrome = false;
            break;
        }
    }
    // print result
    if(isPalindrome) {
        cout << "String is palindrome" <<endl;
    } else{
        cout << "String is not palindrome" <<endl;
    }
}

The program uses length() function of String class to get the length of the string.
Notice the statement if(s[i] != s[length - i - 1]) which compares the character at the left side with the character at the right.
As soon as it finds a mismatch, it sets the bool variable to false and terminates the loop.
Output

Method 2
This method is similar to above method but it uses C-style string to store the string in a character array and it uses two variables to access the characters at the left and right of the string.
Variables i and j are used for left and right characters respectively.
i is initialized to 0 which means that it points to the first character.
j is initialized to length of string – 1, which means that it points to the last character of string.
In every loop iteration, i is increased while j is decreased by 1 and the characters at i^th and j^th indexes are compared.
If they are not same at any point, the string is not palindrome.

#include <iostream>
#include <cstring>

using namespace std;

int main()
{

    char s[50];
    cout << "Enter a string" << endl;
    cin.get(s,50);
    int length = strlen(s);
    bool isPalindrome = true;
    for (int i = 0, j = length - 1; i < length; i++, j--)
    {
        if(s[i] != s[j]) {
            isPalindrome = false;
            break;
        }
    }
    if (isPalindrome)
    {
        cout << "String is palindrome" << endl;
    }
    else
    {
        cout << "String is not palindrome" << endl;
    }
}

Output

Method 3
This method uses two string objects. One object contains the string that needs to be checked and second contains the reversed string.
Input string is reversed using a for loop which traverses the string in reverse direction and assigns each character to the second string.
After the loop completes, the second string contains the input string in reverse order. Both these strings are then compared using compare() function of String class.
compare() will return 0 if the strings are same.

#include <iostream>
#include <string>

using namespace std;

int main()
{
    cout <<  "Enter a string" << endl;
    // for input string
    string s = "";
    // for reverse string
    string reverse = "";
    // read input string
    getline(cin, s);
    int length = s.length();
    /* make the reverse string array
    of same size as input string */
    reverse.resize(length);
    for(int i = 0,j = length-1; i < length; i++,j--){
        reverse[i] = s[j];
    }
    // compare input and reversed strings
    if(s.compare(reverse) == 0) {
        cout << "String is palindrome" << endl;
    } else{
        cout << "String is not palindrome" <<endl;
    }
}

Notice the use of resize() function invoked on the reverse string object.
This function is passed the length of input string and is used so that the size of array used to store reversed string becomes the same as the input string and they are compared correctly.
Output

Hope the article was useful.