c++ - Why does my Palindrome function keep returning false? -

i have text file consists of:

1457887541  madam  able ere saw elba  straw? no, stupid fad. put soot on warts.  class cancelled today 

and when run program, strings returning false , can't figure out why is.

#include <iostream> #include <fstream> #include <string> #include <cstring> #include <cctype>  using namespace std;  bool ispalindrome(string);  int main() { string input; fstream namefile;   namefile.open("xample.txt", ios::in);   if (namefile) {    cout << "now reading file: " << endl;    // read item file.    getline(namefile, input);     // while last read operation     // successful, continue.    while (namefile)    {    cout << input << endl;   //palindrome function call   if(ispalindrome(input)){     cout << "it palindrome :)/> " << endl;        }   else {     cout << "it not palindrome :'( " << endl;   }     // read next string.    getline(namefile, input);    }    //close when completed    cout << "done!" << endl;    namefile.close();  }  else {   cout << "error: cannot open file.\n"; } return 0; }    bool ispalindrome(string input){   int first = 0; int last = input.length() - 1;    //begin loop compare first position last while(last > first){ //loop if not number or letter while(!isalnum(input[first]) && !isalnum(input[last])){     first++;     last--;     } if(tolower(input[first]) != tolower(input[last])){     return false;     }  last--; first++;  }   return true;      } 

without running/debugging code, think problem in algorithm. part of code looks it's designed around problem of spaces , punctuation.

//loop if not number or letter while(!isalnum(input[first]) && !isalnum(input[last])){     first++;     last--; } 

that doesn't work though. you're skipping both current first , last character if both of them not alphanum characters, should skip 1 or other of time, should separate out 2 if statements instead of 1 loop.