Palindromes...but determining using variables

[patsfan4878]

Hello again all. Got a question concerning palindromes. Basically I am writing a program that will determine if a line is a palindrome or not, neglecting spaces and punctuation that is. Now I am trying to do this by setting two variables on each end of the string and comparing the two. Now I can compare the first two fine using an if, but I'm a little unclear as to how I would increase my said variables, and then disregard punctuation and spaces. I know that i would need to use a while loop but I dont know what arguments to use. Thanks for the help.

*Edit*
Scratch that, did some more research which solved some of my problem, but still am lacking on how to remove punctuation and spaces.

[Hamrick]

Just don't compare the two variables if one is a space or punctuation.

while ( i < j ) {
  if ( isvalid( string, i ) && isvalid( string, j ) ) ) {
    if ( string[i++] != string[j++] ) {
      printf( "Not a palindrome\n" );
      break;
    }
  }else {
    if ( !isvalid( string[i] ) ) {
      ++i;
    }

    if ( !isvalid( string[j] ) ) {
      ++j;
    }
  }
}

isvalid is a placeholder for whatever you write to test that a character isn't a space or punctuation.