带提示的两个数字的总和 [英] Sum of two numbers with prompt

问题描述

最近几天，我一直在尝试解决此问题:当我通过提示符将输入的两个数字相减，相乘或相除时，一切正常.但是当我要添加它们时，我得到了两个简单地写在一起的数字.

I've been trying to solve this problem for the last couple days: when I subtract, multiply or divide 2 numbers input through a prompt, everything works fine; but when I want to add them, I get the 2 numbers simply written together.

示例:如果我加5和6，我得到56 ！！

Example: if I add 5 and 6, I get 56!!

这是我正在使用的代码.

Here's the code I'm working with.

var a = prompt("Enter first number");
var b = prompt("Enter second number");

alert(a + b);

我做错了什么?我必须指定值类型吗?

What am I doing wrong? Do I have to specify the value type?

推荐答案

函数prompt返回字符串，并且+(可能不明智地)用于两者字符串连接和数字加法

The function prompt returns a string and + is (unwisely, perhaps) used for both string concatenation and number addition.

您没有在JavaScript中指定类型"，但是可以在运行时进行字符串到数字的转换.有很多方法可以做到这一点.最简单的是:

You do not "specify types" in JavaScript but you can do string to number conversion at run time. There are many ways to so this. The simplest is:

var a = +prompt("Enter first number");
var b = +prompt("Enter second number");
alert(a + b);

但您也可以

var a = Number(prompt("Enter first number"));
var b = Number(prompt("Enter second number"));
alert(a + b);

(避免使用parseInt，因为它仅处理前导字符，并且不会添加4.5和2.6之类的数字.)

(Avoid parseInt because it only handles the leading characters and will not add numbers like 4.5 and 2.6.)

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