function - Comparing two passwords for validation in C++ -

i trying compare 2 c++ strings. function passes old password compared new password. condition new password first half of new password , old password cannot same , second half of new password , old password cannot same. example, if old password abcdefgh , new password abcdyzyz, new password not accepted since first half of these passwords same. have come far , runs display doesn't show output statement. comparing them correctly?

bool changepassword(string& password) { string newpw; int lengthnewpw; int lengtholdpw; float sizen; float half;  {     cout << "enter new password: ";     getline(cin, newpw);        lengthnewpw = newpw.length();     lengtholdpw = password.length();     if (lengthnewpw < lengtholdpw)     {         sizen = lengthnewpw;     }     else if (lengtholdpw < lengthnewpw)     {         sizen = lengtholdpw;     }     else         sizen = lengtholdpw;       half = sizen / 2;      if (newpw.compare(0, half - 1, password) == 0 || newpw.compare(half, (sizen - half) - 1, password) == 0)    {        cout << "the new password cannot start or end " << half << " or more characters same old password" << endl << endl;    }   } while (newpw.compare(0, half - 1, password) == 0 || newpw.compare(half, (sizen - half) - 1, password) == 0 );  return true; } 

try:

bool changepassword(const string& password) {     for( ; ; )     {         string newpw;         cout << "enter new password: ";         getline( cin, newpw );          size_t half = ( newpw.length() < password.length() ? newpw.length() : password.length() ) >> 1;         // may want to add: if( !newpw.empty() )         if( ( password.size() <= 2 ) ||             ( ( password.substr( 0, half ) != newpw.substr( 0, half ) ) &&               ( password.substr( password.size() - half ) != newpw.substr( newpw.size() - half ) ) ) )             return true;  // <-- ever return non-true?  max retries?          cout << "the new password cannot start or end " << half << " or more characters same old password" << endl << endl;     }     return true; }