function validateCat(document) {
  allowed_chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ,-_ ";
  category = document.getElementsByName('f_category')[0].value;
  var allValid = true;

  for (i=0; i < category.length; i++) {
    ch = category.charAt(i);
    for (j=0; j < allowed_chars.length; j++) {
      if (ch == allowed_chars.charAt(j)) break;
      if (j == allowed_chars.length-1)
      {
        allValid = false;
        break;
      }
    }
  }
  if (category.length == 0) {
    allValid = false;
  }

  if (allValid == false) {
    alert ("Please enter valid input.");
  }
  return allValid;
}

function validateLogin(document) {
  allowed_chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
  username = document.getElementsByName('f_username')[0].value;
  var allValid = true;

  for (i=0; i < username.length; i++) {
    ch = username.charAt(i);
    for (j=0; j < allowed_chars.length; j++) {
      if (ch == allowed_chars.charAt(j)) break;
      if (j == allowed_chars.length-1)
      {
        allValid = false;
        break;
      }
    }
  }
  if (username.length == 0) {
    allValid = false;
  }

  if (allValid == false) {
    alert ("Please enter valid username.");
  }
  return allValid;
}