for文・if文・Math/Dateオブジェクト

課題

Q1

<!DOCTYPE HTML>
<html lang="ja">
<head>
<meta charset="utf-8">
<title>課題1</title>
</head>
<body>
<script>
for(var i=1; i<=3; i++){
  alert(i);
}
</script>
</body>
</html>

Q2

<!DOCTYPE HTML>
<html lang="ja">
<head>
<meta charset="utf-8">
<title>課題2</title>
</head>
<body>
<script>
var point;
point=prompt('点数を入力してください。','半角数字で0〜100まで');
alert(point>=70?'合格':'不合格');
</script>
</body>
</html>

Q3

<!DOCTYPE HTML>
<html lang="ja">
<head>
<meta charset="utf-8">
<title>課題3</title>
</head>
<body>
<script>
var rnd=Math.random();

if(rnd<=0.33){
	var msg='今日はラッキーデー！';
	}else if(rnd<=0.66){
		var msg='今日はいい感じ！';
	}else{
		var msg='ボチボチがんばろう！';
		}
		document.write(msg);
</script>
</body>
</html>

Q4

<!DOCTYPE HTML>
<html lang="ja">
<head>
<meta charset="utf-8">
<title>課題4</title>
</head>
<body>
<p><img src="http://placehold.it/550x360" id="change" alt="#"></p>
<script>
var today;
var hour;
today=new Date();
hour=today.getHours();

if(hour<=6){
	document.images['change'].src='01.jpg';
}else if(hour<=12){
	document.images['change'].src='02.jpg';
	}else if(hour<=28){
	document.images['change'].src='03.jpg';
	}else if(hour<=24){
	document.images['change'].src='04.jpg';
	}
</script>
</body>
</html>

Q5

<!DOCTYPE html>
<html lang="ja">
<head>
<meta charset="UTF-8">
<title>画像をランダムに変更して表示する</title>
</head>
<body>
<script>
var img;
img = new Array();
img[0] = '01.jpg';
img[1] = '02.jpg';
img[2] = '03.jpg';
img[3] = '04.jpg';
img[4] = '05.jpg';
n = Math.floor(Math.random()*img.length);
document.write( '<p><img src="' + img[n] + '"></p>' );
</script>
</body>
</html>