function init() {
  var question = [
    ["12×3", 6, 0, 3, 0, 36],
    ["26×2", 12, 1, 4, 0, 52],
    ["43×3", 9, 0, 12, 1, 129],
    ["65×5", 25, 2, 32, 3, 325],
    ["87×9", 63, 6, 78, 7, 783]
  ];
  var j;
  var i = 0;

  function calc() {
    for (j = 1; j < 6; j++) {
      var anser = document.getElementById('q' + j).value;
      if (anser == question[i][j]) {
        document.getElementById('a' + j).innerHTML = "○";
      } else {
        document.getElementById('a' + j).innerHTML = "×";
      }
    }
  }

  function next_q() {
    document.anserform.reset();
    for (j = 1; j < 6; j++) {
      document.getElementById('a' + j).innerHTML = "";
    }
    i++;
    document.getElementById(question).textContent = question[i][0];
  }
  var ans = document.getElementById('ans');
  ans.addEventListener('click', calc);

  var next = document.getElementById('next');
  next.addEventListener('click', next_q);
}
window.onload = init();