Working with Numbers

Rust is a typed language, every variable must specify its type. The common number types are integers i32, i64, u32, u64, f64. The 32/64 is for the bit sized, i for signed integer, u for unsigned integer, and f for float.

Basic Math

fn main() {
    let x = 3;
    let y = 6;
    println!("{} + {} = {}", x, y, x + y);
    println!("{} * {} = {}", x, y, x * y);


String to Integer

To convert a string to an integer in Rust, use parse() function. The parse function needs to know what type, which can be specified on the left-side of assignment like so:

let str = "123";
let num: i32 = str.parse().unwrap();

You can also specify the parse type inline, using ::<> syntax:

let str = "123";
let num = str.parse::<i32>().unwrap();

📌 Note: The use of .unwrap() is to "catch" the potential error and fail at this point.

String to a Float

To convert a string to a float in Rust, uses the same parse() function. You just specify f64 for the type.

let pi = "3.14159";
let num: f64 = pi.parse().unwrap()

Char to a Integer

To convert a single char to an integer in Rust, use .to_digit(RADIX). The radix value is used for conversion, 10 for decimal, 16 for hexadecimal.

let ch = '2';
let num = ch.to_digit(10).unwrap();
let ch = 'f';
let num = ch.to_digit(16).unwrap();
println!("{}", num);
// 15

Integer to String

To convert an integer to a string in Rust, use .to_string()

let num = 123;
let str = num.to_string();

Integer to Float

To convert an integer to a float in Rust, use as f64. This is a useful means to convert from various interchangeable types, you can use inline also.

let num = 13;
let flt = num as f64;
println!("{}", 1.2 * flt);
println!("{}", 1.2 * num as f64);

Float to Integer

Use the same as to cast a float to an integer type. By default, it will discard the decimal portion of the number giving you an equivalent of floor(). Use .round() or .ceil() prior to control how you want the float to be converted.

let num = 13.6 as f32;
let i = num as i32;
let j = num.round() as i32;
let k = num.ceil() as i32;
println!("{} {} {}", i, j, k);