Table of contents
The execution flow of the for loop
Commonly used for arrays and objects
Execution flow of do-while loop
1. for loop
grammar:
for (initialization statement; conditional judgment; conditional control statement) {
loop execution statement
}
The execution flow of the for loop:
①Execute the initialization statement
② Execute the conditional judgment statement to see if the result is true or false
If false, end the loop
If true, continue looping
③ Execute the loop body statement
④Execute conditional control statement
⑤ Go back to ② to continue the cycle
2. for in loop
Commonly used for arrays and objects
Syntax:
for (variable in object) { loop execution statement}
3. while statement
grammar:
initialization statement
while (conditional judgment statement) {
loop statement;
conditional control statement;
}
Small exercises on Mount Everest:
<script>
// 定义一个计数器，初始值为0
let sum = 0;
// 定义纸张的厚度
let paper = 0.1;
// 定于珠峰的高度
let zf = 8844430;
// 循环条件：纸张的高度小于等于珠峰的高度才能继续执行
while(paper <= zf){
// 循环执行的过程中，每次纸张的折叠，厚度加倍
paper *= 2;
// 对应折叠多少次
sum++
}
document.write('需要折叠: '+ sum +'次')
</script>4. do-while statement
grammar:
initial judgment
do{
loop statement;
conditional control statement;
}while (conditional judgment statement) ;
The execution flow of the do-while loop:
The program is executed from top to bottom
①Execute the initialization statement
② Execute the loop body statement
③Execute conditional control statement
④ Execute the conditional judgment statement to see if the result is true or false
If false, end the loop
If true, continue looping
⑤ Go back to ② to continue the cycle
<script>
let i = 1;
do{
document.write(i+'<br>')
i++
}while(i<=5)
</script>5. Double for loop
Each loop can be nested with each other, generally no more than three layers
★The outer loop variable changes once, and the inner loop variable needs to be changed once
The following is a small practice of the ninety-nine multiplication table:
<script>
for(var i = 1;i <= 9;i++){
for(var j = 1;j <= i;j++){
if((i*j)<10){
document.write(j + '*' + i + '=' + i * j +' ')
}
document.write(j + '*' + i + '=' + i * j +' ')
} document.write('<br>')
}
</script>