var texttypes = new Array(1);
   var errortypes = new Array(3);

   function initialize() {
      
      texttypes[0] = document.mainform.elements[0];
      
      errortypes[0] = "Please enter your zip code.";
      errortypes[1] = "Please enter a valid zip code.";
      errortypes[2] = "Zip code format is 99999.";

      exp0 = /^[1-9][0-9]{4}$/;

   }

   function validate() {

      initialize();
      
      if (texttypes[0].value == "") {

         alert(errortypes[0]);
         return false;

      }

      if (isNaN(texttypes[0].value)) {
                
         alert(errortypes[1]);
         return false;

      }

      if (texttypes[0].value.search(exp0) == -1) {

         alert(errortypes[2]);
         return false;

      }
           
    
      return true;
   
   }