javascript 如何将两个数字相加？

How to add two numbers?

提问by Pramito Rahman

I wrote a JavaScript calculator... but suppose when I give my first number as 2and the second number as 3, the result is showing 23, but I wanted to add the two numbers.

我写了一个 JavaScript 计算器……但是假设当我给我的第一个数字 as2和第二个数字 as 时3，结果显示为23，但我想将这两个数字相加。

Can anyone please help me? It is also happening when I try to minus the two numbers. Why isn't this working?

谁能帮帮我吗？当我尝试减去这两个数字时，也会发生这种情况。为什么这不起作用？

var cal = prompt("Please enter what type of calculation you want to do\n
if you wanna add enter = 1\n
if you want to minus enter = 2\n
if you want to divide enter = 3\n
if you want to multiply enter = 4");

if (cal == 1) {
    var a = prompt("Please enter your first number");
    var b = prompt("please enter your second number");

    alert("The result is , " + a+b);
}

if (cal == 2) {
    var c = prompt("Please enter your first number");
    var d = prompt("please enter your second number");

    alert("the result is , " + c - d);
}

采纳答案by Satpal

Try this:

试试这个：

var cal = prompt("Please enter what type of calculation you want to do\n" +
  "if you want to add enter = 1\n" +
  "if you want to minus enter = 2\n" +
  "if you want to divide enter = 3\n" +
  "if you want to multiply enter = 4");

if (cal == 1) {
    var a = prompt("Please enter your first number");
    var b = prompt("please enter your second number");

    alert("The result is , " + (Number(a) + Number(b)));
}

else if (cal == 2) {
    var c = prompt("Please enter your first number");
    var d = prompt("please enter your second number");

    alert("the result is , " + (Number(c) - Number(d)));
}

回答by Danny Beckett

The +sign is used to concatenate strings together, not to add them together mathematically.

该+符号用于将字符串连接在一起，而不是在数学上将它们相加。

You need to wrap your variables in parseInt(), e.g.

您需要将变量包装在parseInt()，例如

alert("The result is , " + parseInt(a)+parseInt(b));

回答by zerkms

Convert a string to a number after you accept it from user:

从用户接受字符串后，将字符串转换为数字：

a = parseInt(a, 10);

回答by Michael Robinson

Prompts return strings, you need to parse them as integers (you could also do floats using parseFloat)

提示返回字符串，您需要将它们解析为整数（您也可以使用浮点数parseFloat）

alert("The result is , " + (parseInt(a) + parseInt(b)));

alert("The result is , " + (parseInt(a) + parseInt(b)));

回答by Vijendra Singh

The Promptmethod returns the entered value as a string.

该Prompt方法将输入的值作为字符串返回。

So after Promptuse parseInt(), this function parses a string and returns an integer.

所以在Prompt使用之后parseInt()，这个函数解析一个字符串并返回一个整数。

回答by PleaseStand

The binary+operatorhas two uses: addition and string concatenation. Although you want the former, the latter is happening because window.prompt()returns a string.

该二进制+运算符有两个用途：加法和字符串连接。虽然你想要前者，但后者正在发生，因为window.prompt()返回一个字符串。

To avoid this, you should do one of the following (read the documentation so you can understand the differences):

为避免这种情况，您应该执行以下操作之一（阅读文档以了解差异）：

• Parse the strings as integers using parseInt(str, 10).
• Parse the strings as floating-point numbers using parseFloat(str).
• Cast the strings to numbers using the unaryplus operator: +str.
• Alternatively, Number(str)can be used.

• 使用 将字符串解析为整数parseInt(str, 10)。
• 使用 将字符串解析为浮点数parseFloat(str)。
• 使用一元加号运算符将字符串转换为数字：+str。
• 或者，Number(str)可以使用。

It is wise to check whether the numbers could be parsed (using isNaN(num), or possibly num === num) before trying to perform calculations with them, so your script can show a helpful error message instead of just carrying NaNthrough to its output.

在尝试使用它们执行计算之前检查数字是否可以解析（使用isNaN(num)或可能num === num）是明智的，这样您的脚本可以显示有用的错误消息，而不仅仅是执行NaN到其输出。

回答by Saiyam

Use:

利用：

var add = parseFloat(a)+parseFloat(b);

回答by zeeshan

num1 = window.prompt("Please Enter Your Num1 :");
num2 = window.prompt("Please Enter Your Num2 :");
var sum = parseInt(num1)+ parseInt(num2);
document.writeln("<h1> The summ of two integers,"+num1+", and,"+num2+", is ,"+sum+",</h1>"  )

I Hope this will help you.

我希望这能帮到您。

回答by zeeshan

You are adding to Strings; known as concatenation, you need to convert the String representations to numbersthen add them.

您正在添加字符串；称为串联，您需要将字符串表示形式转换为数字，然后将它们相加。

alert("The result is , " + (parseInt(a) + parseInt(b)));

回答by Tamil Selvan C

Use

利用

alert("The result is , " + (parseFloat(a)+parseFloat(b)));