Average finder总是打印“0”

Question

我正在尝试创建一个程序，该程序可以找到某人输入的一组数据的平均值。我试过使用下面的代码：

var data = [];
var yesno = confirm("Would you like to add more data?");
while (yesno) {
  var newdata = prompt("Enter a piece of data (must be a number)");
  data.push(newdata);
  var yesno = confirm("Would you like to add more data?");
}
var total = 0;
var i = 0;
if (!yesno) {
  while (i < data.length) {
    total + data[i];
    i++;
  }
  var average = total / data.length;
  document.write(average);
}

但是，当我运行它时，无论我放入什么，它总是打印“0”。提前感谢您的帮助。

Answer 1

问题出在这条线上

total + data[i];

此代码将在某些结果将生成时执行。但随后该值不会发生任何变化。在javascript中，数字是基本类型。除对象以外的所有数据类型对象。你不能用=来改变它们(给它们赋值)。

您需要使用赋值表达式。

total = total + data[i]; 

或者简称为

total += data[i]; 

另一个问题是您没有将prompt()的结果转换为Number。使用一元加+将字符串转换为数字。

下面是你的代码的修正版本。

​

var data = [];
var yesno = confirm("Would you like to add more data?");
while (yesno) {
  var newdata = +prompt("Enter a piece of data (must be a number)");
  data.push(newdata);
  var yesno = confirm("Would you like to add more data?");
}
var total = 0;
var i = 0;
if (!yesno) {
  while (i < data.length) {
    total += data[i];
    i++;
  }
  var average = total / data.length;
  document.write(average);
}

​

使用do-while和reduce()可以实现更干净、更好的版本

​

var data = [];
var yesno;
do{
  var newdata = +prompt("Enter a piece of data (must be a number)");
  yesno = confirm("Would you like to add more data?");
  data.push(newdata);
}
while (yesno);
var total = data.reduce((ac,a) => ac + a,0);
var average = total / data.length;
document.write(average);

​

Answer 2

total + data[i]是一个“孤立表达式”。使用=或+=。

​

var data = [];
var yesno = confirm("Would you like to add more data?");
while (yesno) {
  var newdata = +prompt("Enter a piece of data (must be a number)");
  data.push(newdata);
  var yesno = confirm("Would you like to add more data?");
}
var total = 0;
var i = 0;
if (!yesno) {
  while (i < data.length) {
    total += data[i];
    i++;
  }
  var average = total / data.length;
  document.write(average);
}

​

Answer 3

试试这个：

var data = [];
var yesno = confirm("Would you like to add more data?");
while (yesno) {
    var newdata = prompt("Enter a piece of data (must be a 
    number)");
    data.push(newdata);
    var yesno = confirm("Would you like to add more 
    data?");
}
var total = 0;
var i = 0;
if (!yesno) {
    while (i < data.length) {
        total += data[i];
        i ++;
        var average = total / data.length;
document.write(average);
        } 
    }