Checking if alphabetic string is a palindrome in C++ - c++

Question

I've attempted to write a code that checks whether or not a string is a palindrome. Here is the code:
#include <iostream>
#include <string>
using namespace std;
bool pal(string str)//This block of code checks if input string is a palindrome
{
bool valid;
int i;
for (i = 0; i < str.length(); i++)
{
if (str[-i] == str[i])
{
valid = true;
}
else
{
valid = false;
}
}
return valid;
}
int main()
{
string s;
cin >> s;
if (!pal(s))
{
cout << "NO" << endl;
}
else
{
cout << "YES" << endl;
}
return 0;
}
Currently I am getting "Debug Assertion Fail" error.

Answer 1

str[-i] == str[i]
is a problem since negative indices are not valid indices in C++.
You need to change the strategy a little bit.
bool pal(string str)
{
int i = 0;
int j = str.length() - 1;
for ( ; i < j; ++i, --j)
{
if (str[i] != str[j])
{
// No need for any more checks.
return false;
}
}
// If we come here, the string is a palindrome.
return true;
}

Answer 2

C++ Provides us with an inbuilt function reverse() which can be used to reverse the Input string and compare it with un reversed string and print the output. The code goes as follows.
#include<iostream>
#include<algorithm>
using namespace std;
int main(){
string str;
cin>> str;
string rev;
rev = str;
reverse(str.begin(), str.end()); // string reverse operation
if(rev == str){
cout<<"YES"<<endl; // Prints "Yes" if string is palindrome
}else{
cout<<"NO"<<endl; // Prints "No" if string is not palindrome
}
return 0;
}