你如何用javascript编写一个程序，要求用户输入一个数字列表，然后找到数字的平均值

Question

我无法让这个程序输出用户输入的提示数字的平均值。我还应该如何编码？任何帮助将不胜感激。

var gpas = [];
var gp;
var total = 0;
let count = 0;
var max = 0;
var min = 0;
var out = "";
while (i != "XXX") {
    var i = prompt("Enter a gpa or XXX to Stop");
    if (i != "XXX") {
        gpas.push(i);
    }
}
for (var i = 0; i < gpas.length; i++) {
    out += gpas[i];
    out += "<br/>";
}
count++;
total += gpas[i];
var avg = total / count;
out += avg;
document.getElementById('output').innerHTML += out + "<br/>";

输出显示“NaN”而不是有效数字。

Answer 1

您只能使用一个变量来保存输入数字的总和，然后将其除以输入的总数。

第一种方法无限循环：

第一种方法是您正在使用的方法。基本上，只要我们没有得到字符串"XXX"，我们就会要求一个新号码。

/** 
* @const output the span where to print the average.
**/
const output = document.getElementById('output');

/**
* @var avg stores the sum of the entered numbers.
* @var i keeps track of the number of numbers entered.
**/
let sum = 0,
  i = 0;
  
/** basically while true increment i **/
while (1 && ++i) {
  /** ask for a number or "XXX" to exit **/
  const n = prompt(`Enter a number or enter "XXX" to exit :`, 0);
  /** if "XXX" is entered break the loop (the only way to break that infinite loop) **/
  if(n == 'XXX') break;
  /** if something else than "XXX" is entered try to cast it to a float  **/
  sum += parseFloat(n);
}

/** print the average **/
output.textContent = (sum / (i - 1)).toFixed(2); /** why dividing by "i - 1" and not only "i" is because "i" is incremented even when we enter "XXX" **/

<div>average: <span id="output"></span></div>

这种方法对用户不友好（除非输入"XXX"，否则无法退出循环）并且可能会消耗大量资源。

第二种方法固定数量的数字：

这种方法要求用户输入他想输入的数字，然后我们要求他输入与他之前输入的数字一样多的数字。

const output = document.getElementById('output');

/**
* @var n the number of numbers the user is going to type.
* @var sum the sum of these numbers.
* @var i a counter used to exit the loop when we reach "n" nummbers typed. 
**/
let n = prompt('How many element do you want to enter ?', 2),
  sum = 0,
  i = 0;
  
/** while i + 1 < n and no need to manually break the loop **/
while (i++ < n) sum += parseFloat(prompt(`Enter a number (${i} remaining) :`, 0));

output.textContent = (sum / n).toFixed(2); /** now we know how many numbers entered from the beging thanks to the variable "n" **/

<div>average: <span id="output"></span></div>

parseFloat 用于将用户输入的数字（实际上是字符串）解析为浮点数。

toFixed 用于计算平均值时只有两位小数。

Answer 2

while (i != "XXX") {
    var i = prompt("Enter a gpa or XXX to Stop");
    if (i != "XXX") {
        gpas.push(parseInt(i)); // we need string to number with `parseInt`
    }
}

Answer 3

感谢所有做出贡献的人。通过应用给出的一些建议，我能够让它发挥作用。我还注意到下面的代码也可以工作：

 var gpas = [];
 var gp;
var out = "";
while (i != "XXX")
{
var i = prompt("Enter a gpa or XXX to Stop");
if(i != "XXX"){
gpas.push(parseInt(i));
}
}  
     let sum = gpas.reduce((a, b) => {
 return a + b;
}); 

sum;
var avg = (sum/gpas.length);
document.getElementById('output').innerHTML += "average =" + avg + "<br/>";
</script>````