What are the structures of JavaScript programs?

There are three types of program structures in JavaScript, namely: 1. Sequential structure; by default, the program is executed line by line from top to bottom. 2. Branch structure; depending on the results of conditional judgment, selective execution is different. 3. Loop structure: the program can execute the same code segment repeatedly and exit when it reaches a critical point.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

The program structure in JavaScript

is divided into three major categories:

• Sequence: The program is executed line by line from top to bottom by default

• Branch: Depending on the result of conditional judgment, different executions are selectively performed.

• Loop: The program can execute the same code segment repeatedly and exit when it reaches the critical point

****************************************** *************************************************** *********

Example:

Requirement analysis:

var price=prompt("please input the goods price:");
var accout=prompt("please input the goods account:");
var money=prompt("please input the goods money:");
var sum=parseFloat(price)*parseInt(accout);
(sum>500)&&(sum*=0.8);
var change=money-sum;
alert("应收"+sum+",找零"+change);

Branch structure

1.if Structure:

Syntax:

if（条件）{
满足条件才执行的的代码段
}

2.if ···else structure:

Syntax:

if（条件）{
满足条件才执行的的代码段}
else{
条件不满足
}

3.else if structure

Grammar:

if（条件1）{
满足条件1才执行的的代码段
}else if（条件2）{
条件2满足
}else if（条件3）{
条件3满足
}else{
之前所有条件都不满足
}

4. Branch structure vs trinocular/short circuit

If you just return the value-->trinocular/short circuit

If the operation is complex--->Branch structure

Short-circuit logic:

Conditions && Operation: If one thing is satisfied, do it, otherwise do not do it , only when the operation is simple

Value 1||Value 2: If value 1 is valid, return value 1, otherwise return value 2

Ternary operation:

Ternary operation: multiple values, judge based on conditions, select one from more than one

条件表达式 ? 表达式1 : 表达式2 ;

If the result of "conditional expression" is true (true), execute "expression 1" code in "Expression 2", otherwise the code in "Expression 2" will be executed.

5.switch structure

Syntax:

switch（表达式）{
case  值1：代码1;
case  值2：代码2;
case  值3：代码3;
"""""`
default:默认代码段;
}

• break: Stop the execution of the current structure , and jump out of the current structure

• continue: end this cycle and continue the next cycle//Control can generally use negative conditions instead.
  

• switch: When the condition is congruent comparison, switch case is preferred

• else if: In addition to congruent comparison, when you want to define the condition flexibly

Loop structure

Loop structure: Let the program repeatedly execute a section of code, and only stop looping when critical conditions are reached

3 elements :

• 1. Loop condition: condition for continuing the loop
  

• 2. Loop variable: used for comparison in the loop condition Variables

  //Start from the number, increase or decrease by the number each time, and end at the number
  

• 3. Loop body: code segment that is executed repeatedly

while loop

Usage conditions: When the change pattern of the loop variable is uncertain

Grammar

while（条件）{
循环体;
迭代循环变量;
}

Example:

Guess the number game: The computer randomly generates a number from 0 to 100. The player guesses the size of the number and is given a hint if the guess is too high or too small. , until you guess it right at the end!

var n=parseInt(Math.random()*(100-0+1)+0);
//生成0-100的随机数
var input="";
while(input!=n&&input!="exit"){
input=prompt("you guess");
alert(
    input>n?"bigger":
    input <n?"smaller":
    input=="exit"?"give up!":
    "you are right"
);

do while loop

Use conditions: If the first condition is not met, we hope it can be executed at least once;

Syntax:

var 循环变量=初值;
do{
  循环体;
  迭代变化循环变量;
} while（循环条件）

for loop

Usage conditions: When the change pattern of the loop variable is fixed

Syntax:

var 循环变量=初值；
for（var 循环变量=初值;循环条件;迭代变化循环变量）{
循环体
}

Example: Print a row in the multiplication table (must be output on the console)

<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<script type="text/javascript">
           function fun(n){
	           var str="";
	           for(var i=1;i<=n;i++){
	           	  str+=( i+"x"+n+"="+(i*n)+" ");
	           }
	           console.log(str);
           }
		</script>
	</head>
	<body>
		<button οnclick="fun(prompt(&#39;请输入行号：&#39;))">打印乘法口诀指定行</button>
	</body>
</html>

[Recommended learning: javascript advanced tutorial]

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