【问题标题】：How to calculate the factorial of a number entered by user in Javascript, using, do-loop, while-loop?如何计算用户在Javascript中输入的数字的阶乘，使用，do-loop，while-loop？
【发布时间】：2020-11-02 04:09:27
【问题描述】：
我上一个问题的快速跟进问题。我想在下面添加代码来计算用户在 Javascript 中输入的数字的阶乘。
<!DOCTYPE html>
<html>
<head>
<title>Sum of Numbers</title>
<script>
var numbers = prompt("Enter a number 1-100");
while (numbers!=null && (isNaN(parseInt(numbers)) || parseInt(numbers) >100 || parseInt(numbers) <1)) {
numbers = prompt("Try again.Enter a number 1-100");
}
if (numbers !=null){
alert("Finally you entered a correct number");
var sum = 0;
var numOfLoops = numbers;
var counter = 1;
do {
sum+=counter;
counter++;
}
while (counter<=numOfLoops)
alert ("The sum of numbers from 1 to " + numbers + "is =" +sum);
}
</script>
</head>
<body>
<script>
document.write("<h1>Sum of Numbers</h1>");
document.write("The sum of numbers from 1 to = " + numbers + " is = " +
+ sum + "<br><br>");
</script>
</body>
</html>
【问题讨论】：
标签：
javascript
while-loop
do-loops
【解决方案1】：
While 循环：
const fact=n=>
{
if(n<0) throw 'factorial error on a negative number!'
let r = 1
while(n) r *= n--
return r
}
一边做：
const fact=n=>
{
if(n<0) throw 'factorial error on a negative number!'
let r = 1
do r *= n || 1 // in case of n == 0
while (n--)
return r;
}
完整代码
const
msgPrompt_1 = 'Please enter a number from 0 to 100',
msgPrompt_n = 'Try again.... Enter a number 0-100',
fact = n =>
{
let r = 1
while(n) r *= n--
return r
}
let numValue = parseInt(window.prompt(msgPrompt_1, ''), 10)
while(isNaN(numValue) || numValue > 100 || numValue < 0)
{
numValue = parseInt(window.prompt(msgPrompt_n, ''), 10)
}
alert(`factorial value of ${numValue} is = ${fact(numValue)}` )
【解决方案2】：
如果您想对数字求和，请考虑使用算术级数公式。如果你想得到阶乘，方法如下所示。
如果您想使用循环求和，只需将*= 更改为+=。
While 循环方法
const fact = (n) => {
let res = 1;
while (n > 0) {
res *= n;
n--;
}
return res;
}
fact(5) // 120
在接近时做
const fact = (n) => {
let res = 1;
do {
res *= n;
n--;
} while (n > 0)
return res;
}
fact(3) // 6
这应该可以解决问题。 :)
也许还考虑检查边缘情况，例如 n 是否为负数。
祝你好运。