<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>
<body>
</body>
</html>
<script>
var a=prompt("请输入一个整数","只能是整数");
if(a!=null)
{
var b=isNaN(a);
if(b==false)
{
var c=parseInt(a);
var sum=0;
for(var i=1;i<=c;i++)
{
sum+=i;
}
alert(sum);
}
else
{
alert("输入有误！");
}
}
else
{
}
</script>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
</head>
<body>
请输入一个数字:<input type="text" id="text"/> <input type="button" value="请点击" onclick="add()"/>
</body>
</html>
<script>
function add()
{
var a= document.getElementById("text");
var b=isNaN(a.value);
if(b==false)
{
var c= parseInt(a.value);
var sum=0;
for(var i=0;i<=c;i++)
{
sum+=i;
}
document.write(sum);
}
else
{
alert("输入有误！");
}
}
</script>
