Numbers, booleans and characters

Every value in Rust has a type. Here are the simple ones.

Integers

Whole numbers are integers. i types can be negative; u types can't. The number after the letter is the size in bits.

let x = 42; makes an i32. You can write 1_000_000 to make big numbers easy to read.

Floats

Numbers with a decimal point are floats. The default is f64; f32 is smaller.

1let price = 9.99;   // f642let x: f64 = 1.0;   // write 1.0, not 1

Integer division

Dividing two integers drops the remainder. % gives the remainder.

1println!("{}", 7 / 2);     // 32println!("{}", 7 % 2);     // 13println!("{}", 7.0 / 2.0); // 3.5

bool and char

A bool is true or false. Comparisons give a bool: == (equal), != (not equal), <, >, <= and >=. So 10 > 3 is true. Join bools with && (and) and || (or), and flip one with ! (not).

A char is one character in single quotes, like 'a' or '🦀'. Double quotes, like "a", make text, not a char.

Casting with as

Rust never mixes number types for you. Adding an i32 to an f64, or putting an i32 where an i64 is wanted, is an error. Use as to convert:

1let a: i32 = 5;2let b: f64 = 2.5;3let c = a as f64 + b;  // 7.54let n = 9.99 as i32;   // 9, the decimals are cut off

A char can become its number too: 'A' as u32 is 65.

Remember

• Integers are i32 and floats are f64 unless you say otherwise.
• 7 / 2 is 3, and 7 % 2 is 1.
• char uses single quotes.
• Convert numbers with as.