function doCheck(input) 
{
  if( !input ) {
    input = 0;
  }

  input = parseInt(input);

  if( isNaN(input) ) {
    alert("Only numbers allowed for input values.");
    return 0;
  } 

  if( input < 0 ) {
    alert("Please enter a positive number.");
    return 0;
  }

  if( input < 20) {
    alert("20 or more must be purchased for the discounted price.");
    return 20;
  }

  return input;
}

function setCheck(number) 
{
  number  = doCheck(number);
  document.discount.itemquant.value	= number;

  if( number > 19 ) {
      document.normal.itemquant.value	= 0;
  }
}