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JavaScript JavaScript Basics (Retired) Making Decisions with Conditional Statements Build a Random Number Guessing Game

Posted by Kiran Kumar
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Kiran Kumar
Front End Web Development Techdegree Student 3,793 Points

I have never encountered any zero when using Math.ceil

But why does the teacher use Math.floor and extra code to get the number between 1 - 6?

Teacher's Code:

var randomNumber = Math.floor( Math.random() * 6) + 1;

He said Math.ceil might give you zero sometimes, but I never encountered zero. Math.random() always returns greater value than zero, as long as the value is not less than zero, Math.ceil returns the value of 1.

Code I tried:

var randomNumber = Math.ceil( Math.random() * 6);

Both are working exactly the same way, but I'm confused why the teacher has used Math.floor? Please help

1 Answer

Shunpan Lo
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Shunpan Lo
Full Stack JavaScript Techdegree Student 19,126 Points

Math.random() will return a random number between 0 (inclusive) and 1 (exclusive). Might be you are too lucky that you never meet a 0 value from Math.random(). When Math.random() gives you a 0 value:

Math.floor( Math.random() * 6) + 1 = Math.floor( 0 * 6) + 1 = 0 + 1 = 1

Thus, if you really want to value from 1 to 6. The above formula will be the only answer.

For Math.ceil( Math.random() * 6), when Math.random() gives you a 0 value:

Math.ceil( Math.random() * 6) = Math.ceil(0 * 6) = Math.ceil(0) = 0

You might have a chance getting a zero value but not 1 to 6 only.

Kiran Kumar
.a{fill-rule:evenodd;}techdegree
Kiran Kumar
Front End Web Development Techdegree Student 3,793 Points

That's what I was wondering xD Got it, thanks.