Javascript Input Numbers

Question

How do you take 2 numbers from the User with window.prompt and add them up without concatenating?

What I thought was:

var temp = window.prompt("Number1")
var temp2 = window.prompt("Number2")
var answer = temp + temp2;
document.write(answer);

but it only concatenates not adds.

score 8 · Accepted Answer · answered Nov 23 '10 at 23:42

8

You need to convert the values to Number, there are plenty of ways to do it:

var test1 = +window.prompt("Number1"); // unary plus operator
var test2 = Number(window.prompt("Number2")); // Number constructor
var test3 = parseInt(window.prompt("Number3"), 10); // an integer? parseInt
var test4 = parseFloat(window.prompt("Number4")); // parseFloat

answered Nov 23 '10 at 23:42

Christian C. Salvadó

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Note: To know the differences between the unary plus operator, the `Number` constructor called as a function and `parseInt`/`parseFloat` check [this answer](http://stackoverflow.com/questions/4090518/string-to-int-use-parseint-or-number/4090577#4090577) – Christian C. Salvadó Nov 23 '10 at 23:50
Note 2: Using *no-op* mathematical operations such as `foo * 1;` or `foo - 0` are slightly equivalent to use the unary plus operator or the `Number` constructor called as a function. – Christian C. Salvadó Nov 23 '10 at 23:55

score 0 · Answer 2 · answered Nov 23 '10 at 23:40

0

answer = parseInt(temp) + parseInt(temp2);

is what you're looking for

More information on parseInt: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/parseInt

answered Nov 23 '10 at 23:40

Jason Benson

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Please, don't link to w3schools, that's is by far the worse place one can go to. Link to MDC instead: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/parseInt – Ivo Wetzel Nov 23 '10 at 23:42

score 0 · Answer 3 · answered Nov 23 '10 at 23:41

0

You need to explicitly convert them to numbers:

var answer = Number(temp) + Number(temp2);

A somewhat faster alternative is:

var answer = (temp - 0) + (temp2 - 0);

answered Nov 23 '10 at 23:41

casablanca

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score 0 · Answer 4 · answered Nov 23 '10 at 23:42

0

by default, text from window.prompt is interpreted as string so the + operator concatinates them, you need to parse the values to integers using parseInt

answered Nov 23 '10 at 23:42

Ali Tarhini

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score 0 · Answer 5 · answered Nov 23 '10 at 23:43

The problem is that your input is a string (text) and you have to convert it to a number.

You can do that with the parseInt() function or by mixing it with another number.

Examples:

var temp = window.prompt("Number1") * 1;
var temp = parseInt(window.prompt("Number2");

Javascript Input Numbers

5 Answers5

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