17.JavaScript-循环嵌套练习

1. 循环嵌套规律

在循环嵌套中外循环控制的是行数，内循环控制的是列数

-----------------------------------------------------1---------------------------------------------------------

需求：输出3行 ****

for (let j = 0; j < 1; j++) {
    for (let i = 0; i < 4; i++) {
        document.write("*");
    }
    document.write("<br>");

}

-----------------------------------------------------2---------------------------------------------------------

需求：在界面中输出如下图形(尖尖朝下)
*****
****
***
**
*

for (let i = 0; i < 5; i++) {
    for (let j = i; j < 5; j++) {
        document.write("*");
    }
    document.write("<br>");
}

-----------------------------------------------------3---------------------------------------------------------

需求：在界面中输出如下图形(尖尖朝上)
*
**
***
****
*****

for (let i = 0; i < 5; i++) {
    for (let j = 0; j <= i; j++) {
        document.write("*");
    }
    document.write("<br>");
}

-----------------------------------------------------4---------------------------------------------------------

需求：在界面中输出如下图形
1
12
123

for (let i = 0; i < 3; i++) {
    for (let j = 0; j <=i; j++) {
        document.write(j+1);
    }
    document.write("<br>");
}

-----------------------------------------------------5---------------------------------------------------------

需求：在界面中输出如下图形
1
22
333

for (let i = 0; i < 3; i++) {
    for (let j = 0; j <=i; j++) {
        document.write(i+1);
    }
    document.write("<br>");
}

-----------------------------------------------------6---------------------------------------------------------

需求：输出正三角形
-----*
----***
---*****
--*******
-*********
***********

for (let i = 0; i < 5; i++) {
    for (let j = i; j <5; j++) {
        document.write("-");
    }
    for(let m = 0;m<2*i+1;m++){
        document.write("*");
    }
    document.write("<br>");
}

-----------------------------------------------------7---------------------------------------------------------

需求：输出九九乘法表

for (let i = 1; i <= 9; i++) {
    for (let j = 1; j <=i; j++) {
        document.write(j + "*" + i + "=" + i*j);
    }
    document.write("<br>");
}