playing=false;

function startCounter() {
randomnumber=Math.floor((70 - 20 + 1) * Math.random() + 20);
alert('Generated number is '+randomnumber+'. Match the value!');
if(playing==false) {
    the_time=setInterval('document.starter.timer.value++',100);
  }
  playing=true;
}


function stopCounter() {
  score=Math.abs(document.starter.timer.value-randomnumber);
  document.starter.score.value=Math.abs(document.starter.timer.value-randomnumber);
  if(playing==true&&score<randomnumber) {
    clearInterval(the_time);
    alert('The difference is '+score+'.');
    playing=false;
    if(score==0) {     
 alert('Now Enter Your Name Below!'); 
  document.starter.check.value=0   
    }
  document.starter.timer.value=0;
  }
}