Someone

        // input values which may or may not appear on the form
        var var_array = new Array('china','mobile','thailand','japan','gym','martial_arts','korean_lessons');

        // run through each value, assign the value of 0 to it if it doesn't appear
        for ( i in var_array )
        {
                try {
                        var var_array[i] = document.getElementById(var_array[i]);
                }catch(err){
                        var var_array[i] = 0 ;
                }
        }