JS之语句循环

While语句

Do-While语句

For循环

及他们的练习　　

嵌套

Break语句

Continue语句

九九乘法表

菱形

While语句：

适用于循环次数不确定的。

10以下的偶数和

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>While循环</title>
</head>
<body>

</body>
<script>
    /*1+2+3。。。。+10*/
    var sum = 0;
    var i = 1;              //循环变量的定义
    while (i <= 10) {       //循环变量的判断
        if (i % 2 == 0) {
            sum = sum + i;
        }
        i++;                //循环变量的更新
    }
    alert(sum);
</script>
</html>

求水仙花数：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>水仙花数</title>
</head>
<body>

</body>
<script>
    var i = 1;
    var c;
    var b;
    var s;
    var g;
    while (i < 1000) {
        if (i < 10) {
            g = parseInt(i % 10);
            if (i == g * g * g) {
                alert(c = i);
            }
        }
        if (i < 100 && i >= 10) {
            s = parseInt(i / 10 % 10);
            g = parseInt(i % 10);
            if (i == s * s * s + g * g * g) {
                alert(c = i);
            }
        }
        if (i >= 100 && i < 1000) {
            b = parseInt(i / 100);
            s = parseInt(i / 10 % 10);
            g = parseInt(i % 10);
            if (i == b * b * b + s * s * s + g * g * g) {
                alert(c = i);
            }
        }
        i++;
    }
</script>
</html>

累加求和：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>累加求和</title>
</head>
<body>

</body>
<script>
    var sum = 0;
    var num = parseInt(prompt("请输入整数:"));
    while (num != -1) {
        sum += num;
        num = parseInt(prompt("请输入整数:"));
    }
    alert(sum);
</script>
</html>

Do-While循环：

适用于循环次数不确定的

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>DO-WHILE循环</title>
</head>
<body>

</body>
<script>
    var sum = 0;
    var i = 1;              //循环变量的初始化
    do {
        sum = sum + i;
        i++;                //循环变量的更新
    }
    while (i <= 10);        //循环变量的判断
    alert(sum)
</script>
</html>

10以下的累加

猜数游戏：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>猜数问题</title>
</head>
<body>

</body>
<script>
    var i = 8;
    var num = parseInt(prompt("请输入数字："));
    do {
        if (i > num) {
            alert("小了");
        } else if (i < num) {
            alert("大了");
        }
        num = parseInt(prompt("请继续输入数字："));
    } while (num != 8);
    alert("喝酒")

</script>
</html>

循环的嵌套：

<!--1+（1+2）+（1+2+3）+（1+2+3+4）...-->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>循环的嵌套</title>
</head>
<body>
<!--1+（1+2）+（1+2+3）+（1+2+3+4）...-->
</body>
<script>
    var i = 1;
    var sum = 0;
    while (i <= 5) {
        var j = 1;
        while (j <= i) {
            sum = sum + j;
            j++;
        }
        i++;
    }
    alert(sum);
</script>
</html>

阶乘

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>阶乘</title>
</head>
<body>

</body>
<script>
    var i = 1;
    var sum = 0;
    while (i <= 5) {
        var j = 1;
        var sum2 = 1;
        while (j <= i) {
            sum2 = sum2 * j;
            j++;
        }
        sum += sum2;
        i++;
    }
    alert(sum);
</script>
</html>

For循环：

适用于循环次数确定的。

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>for循环</title>
</head>
<body>

</body>
<script>
    var sum = 0;
    for (var i = 1; i <= 100; i++) {
        sum += i;
    }
    alert(sum)
</script>
</html>

1-10的平方和：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>1-10的平方和</title>
</head>
<body>

</body>
<script>
    var sum = 0;
    for (var i = 1; i <= 10; i++) {
        sum += i * i
    }
    alert(sum);
</script>
</html>

输入一个数字求他的阶乘并展示出来

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>FOR循环</title>
</head>
<body>

</body>
<script>
    var sum = 1;
    var i = parseInt(prompt("请输入数字："));
    for (var q = 1; q <= i; q++) {
        sum *= q;
    }
    document.write(i + "de阶乘结果为" + sum);
</script>
</html>

Break语句：

<!--跳出本次循环，结束循环，不执行所在循环的下面部分-->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>break语句</title>
</head>
<body>
<!--跳出本次循环，结束循环，不执行所在循环的下面部分-->
</body>
<script>
    var sum = 0;
    for (var i = 1; i <= 100; i++) {
        sum += i;
        if (sum >= 2000) {
            alert(i + ":" + sum);
            break;
        }
    }
</script>
</html>

Break语句的嵌套：

<!--1+(1+2)+(1+2+3)+(1+2+3+4)+（1+2+3+4+5）-->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>嵌套循环的break语句</title>
</head>
<body>
<!--1+(1+2)+(1+2+3)+(1+2+3+4)+（1+2+3+4+5）-->
</body>
<script>
    var sum = 0;
    var i = 1;
    while (i <= 5) {
        var j = 1;
        while (j <= i) {
            if (i == 3) {
                break;
            }
            sum += j;
            j++;
        }
        i++;
    }
    alert(sum);
</script>
</html>

Continue语句：

<!--跳过当前循环的剩下部分，执行下一次循环-->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>continue语句</title>
</head>
<body>
<!--跳过当前循环的剩下部分，执行下一次循环-->
</body>
<script>
    var sum = 0;
    for (var i = 1; i <= 100; i++) {
        if (i % 3 == 0) {
            continue;
        }
        sum += i;
    }
    alert(sum);
</script>
</html>

九九乘法表：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>九九乘法表</title>
</head>
<body>

</body>
<script>
    for (var i = 1; i <= 9; i++) {                          //外层循环控制显示的行数
        for (var j = 1; j <= i; j++) {
            var sum = i * j;
            document.write(j + "*" + i + "=" + sum + "  ");
        }
        document.write("<br>");
    }
</script>
</html>

 

菱形：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <style>
        * {
            font-family: "Consolas";        /*定义字体后，菱形比较正*/
        }
    </style>
    <title>菱形</title>
</head>
<body>

</body>
<script>

    //不用绝对值只能用两个for语句来写

    /*for (var i = 1; i <= 4; i++) {
        for (j = 1; j <= 4 - i; j++) {
            document.write("&nbsp");
        }
        for (var k = 1; k <= 2 * i - 1; k++) {
            document.write("*");
        }
        document.write("<br>")
    }
    for (var i = 1; i <= 4 - 1; i++) {
        for (var j = 1; j <= i; j++) {
            document.write("&nbsp");
        }
        for (var k = 1; k <= 2 * 4 - 1 - 2 * i; k++) {
            document.write("*");
        }
        document.write("<br>")
    }*/

    //会用绝对值可以用一个for循环来写

    for (var i = 0; i < 7; i++) {
        for (var j = 0; j < Math.abs(3 - i); j++) {
            document.write("&nbsp;");
        }
        for (var j = 0; j < 7 - 2 * Math.abs(3 - i); j++) {
            document.write("*");
        }
        for (var j = 0; j < Math.abs(3 - i); j++) {
            document.write("&nbsp;");
        }
        document.write("<br>");
    }
</script>
</html>

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原文地址：https://www.cnblogs.com/haloxinghong/p/7277415.html