How do I use std::num::sqrt to compute the square root of a number?

Question

I want to take the square root of a number.

I looked at the documentation here, and wrote use std::num; at the top of my program which I thought would have allowed me to sqrt. This doesn't work though, so what do I need to do to actually use std::num::sqrt?

let upperLimit: i64 = sqrt(num as f64) + 1; //doesnt work

I'm very new to Rust coming from c++, so I really don't understand that real use of use.

Answer 1

Since Rust 1.0, the following should be used:

let upperLimit = (number as f64).sqrt() as i64 + 1;

Or, equivalently:

let upperLimit = f64::sqrt(number) as i64 + 1;

See the docs for f64::sqrt.

Answer 2

Editor's Note: This historical answer predates Rust 1.0 and is no longer applicable.

With use std::num; you "import" the whole module and access members with num::*:

use std::num;

let upperLimit: i64 = num::sqrt(num as f64) + 1;

If you want to use sqrt directly you have to import it as use std::num::sqrt;:

use std::num::sqrt;

let upperLimit: i64 = sqrt(num as f64) + 1;