Valid Palindrome

#include <iostream>
using namespace std;

bool checkPalindrome(const string & rstr)
{
    string fstr;
    int i=0;
    //create string with alphanumerics in small case
    for(auto & ch: rstr)
    {
        if(isalnum(ch))
            fstr+=tolower(ch);
    }
    //cout<<fstr;
    

}


int main() {

    string str;

    getline(cin,str);

    cout<< "The passed str "<<str<< " is valid Palindrome "<<checkPalindrome(str)<< endl;
    return 0;
}