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JS calculate the circumference and area of the circle

2022-04-22 23:13:00 【Did you add pepper?】

subject ： Calculate the circumference and area of a circle

I just studied recently js, Just do the exercises in the book .

<!DOCTYPE html >
<html>
<head>

</head>


<body>
	<!-- Calculate the circumference and area of a circle -->
	<div>
		<p> Perimeter ：<input id="zc" type="text" value=" Perimeter " ></p>
		<p> area ：<input id="mj" type="text" value=" area " ></p>
	</div>
	
<script>
	var a = parseFloat(prompt(" Please enter the radius of the circle ："))
	const p = 3.14 // because Π It is the same. , So I set it as a constant 
	var b = 2*p*a// Perimeter 
	var c = a*p*a// area 
	if(Boolean(a)){
    	// Determine whether it is null 
		
		if( isNaN(a)){
    	// Determine whether it is a value 
		alert(" Input error ")
		}
		else{
    
			document.getElementById("zc").value = b.toFixed(2)//toFixed（2） Simplify two decimal places 
			document.getElementById("mj").value = c.toFixed(2)
		}
		
	}
</script>
   
</body>
</html>