# Check if String is Palindrome in C++

This article will discuss different ways to check if a string is palindrome or not in C++.

There are different ways to do this. Let’s discuss them one by one,

## Check if a string is palindrome using STL Algorithm equal()

To verify if a string is a palindrome, we need to compare the first half with the reversed second half of the String. For example, if String is of length N, then compare,

• Character at index 0 with character at index N-1
• Character at index 1 with character at index N-2
• Character at index 2 with character at index N-3
• ..
• ..
• Character at index n/2-1 with character at index (N-N/2)

If all the above comparisons return true, it means String is a palindrome.

Standard Template Library in C++ provides a function std::equal(). It compares two ranges for element-wise equality, and if all elements in two ranges are equal, it returns true, otherwise false. We can use this to check if String is a palindrome by matching the first half of String with the reversed second half of String i.e.

```#include <iostream>
#include <string>
#include<algorithm>

using namespace std;

/*
This function returns true
if a give string is a palindrome,
otherwise returns false.
*/
bool is_palindrome(string input_str)
{
int len = input_str.length();
return equal( input_str.begin(),
input_str.begin() + len/2,
input_str.rbegin(),
input_str.rbegin() + len/2 );
}

int main()
{
cout<< is_palindrome("abccbad") << endl;
cout<< is_palindrome("abccba") <<endl;
cout<< is_palindrome("abcdcba") <<endl;
cout<< is_palindrome("12abcdcba21") <<endl;
cout<< is_palindrome("87655778") <<endl;

return 0;
}```

Output

```0
1
1
1
0```

Analysis of the Output:

• The string “abccbad” is not a palindrome; therefore, it returned false.
• The string “abccba” is not a palindrome; therefore, it returned true.
• The string “abcdcba” is not a palindrome; therefore, it returned true.
• The string “12abcdcba21” is not a palindrome; therefore, it returned true.
• The string “87655778” is not a palindrome; therefore, it returned false.

## Check if String is palindrome using for loop

If you don’t want to use the equal() function, then you can iterate over the String and compare,

• Character at index 0 with character at index N-1
• Character at index 1 with character at index N-2
• Character at index 2 with character at index N-3
• ..
• ..
• Character at index n/2-1 with character at index (N-N/2)

Where N is the size of String, if all the comparisons return True then it means String is a palindrome. For example,

```#include <iostream>
#include <string>

using namespace std;

/*
This function returns true
if a give string is a palindrome,
otherwise returns false.
*/
bool is_palindrome(string input_str)
{
bool result = true;
int len = input_str.length();
for(int i = 0 ; i < len/2 ; i++)
{
if(input_str[i] != input_str[len -1 -i] )
{
result = false;
break;
}
}
return result;
}

int main()
{
cout<< is_palindrome("abccbad") << endl;
cout<< is_palindrome("abccba") <<endl;
cout<< is_palindrome("abcdcba") <<endl;
cout<< is_palindrome("12abcdcba21") <<endl;
cout<< is_palindrome("87655778") <<endl;

return 0;
}```

Output

```0
1
1
1
0```

## Check if String is palindrome using reverse()

If the reverse of a string is equal to the original String, it means the String is a palindrome. Let’s see how to do that,

```#include <iostream>
#include <string>
#include<algorithm>

using namespace std;

/*
This function returns true
if a give string is a palindrome,
otherwise returns false.
*/
bool is_palindrome(string input_str)
{
std::string new_str(input_str);
std::reverse(new_str.begin(), new_str.end());
return (new_str ==  input_str);
}

int main()
{
cout<< is_palindrome("abccbad") << endl;
cout<< is_palindrome("abccba") <<endl;
cout<< is_palindrome("abcdcba") <<endl;
cout<< is_palindrome("12abcdcba21") <<endl;
cout<< is_palindrome("87655778") <<endl;

return 0;
}
```

Output

```0
1
1
1
0```

Summary

We learned three different ways to check if a string is a palindrome in C++.

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