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JS to determine whether the number entered by the user is a prime number (multiple methods)

2022-06-27 07:35:00 【I am the sun?】

subject ：
The user enters a number , Let's judge whether it is a prime number .
Prime number ： Can only be 1 And the number divisible by itself ,1 It's neither prime nor sum . Prime number must be greater than 1 The natural number of （ Natural number ： 0,1,2,3…）

Method 1 ：

Code ：

<!DOCTYPE html>
<html lang="zh">
<head>
	<meta charset="UTF-8" />
	<meta name="viewport" content="width=device-width, initial-scale=1.0" />
	<meta http-equiv="X-UA-Compatible" content="ie=edge" />
	<title>Document</title>
	<script type="text/javascript">
		var num = +prompt(" Please enter a number ：");
		for(var i = 2;i <= num;i++){
			if(num == i && num != 1)
			{
			document.write(num + " Prime number ");
			break;
}
			else if(num == 1 || num % i == 0 )
			{
				document.write(num + " Not prime ");
				break;
			}	
			
		}
		if(num == 1)
		document.write(num + " Not prime ");
	</script>
</head>
<body>
</body>
</html>

Running results ：
Insert picture description here

Method 2 ：

Make good use of Boolean functions , because fo There is more than one judgment in the loop , therefore , As long as there is one that can 0, Then change to false. Not at last 0, To continue true.
The code is as follows ：

<!DOCTYPE html>
<html lang="zh">
<head>
	<meta charset="UTF-8" />
	<meta name="viewport" content="width=device-width, initial-scale=1.0" />
	<meta http-equiv="X-UA-Compatible" content="ie=edge" />
	<title>Document</title>
	<script type="text/javascript">
		var num = prompt(" Please enter a number ：");
		var flag = true;
		if(num < 1){
			document.write(" Wrong number entered ;");
		}else if(num==1){
			document.write("1 Not prime ");
		}else{
			for(var i = 2;i < num; i++){
			if(num % i == 0 )
			{
			flag = false;
			break;
			}
		}
		if(flag){
			document.write(num + " Prime number ");
		}else{
			document.write(num+" Not prime .");
		}
		}
		
	</script>
</head>
<body>
	
</body>
</html>

The running results are as follows ..

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