Numbers

Start with the idea

Integers and floating-point values model different kinds of information. A signed integer such as i32 can represent negative values; an unsigned type such as u8 uses its bits for nonnegative values. usize is the natural type for an index or collection length because it matches the platform’s address width. f64 represents a broad range of fractional values, but most decimal fractions are approximations in binary, so exact equality is often the wrong test for a measured quantity. None of these types is automatically better: start with what the domain means.

In the example, files is a length-like count, temperature is fractional, and mask is one byte of bit flags. Those annotations tell a reader why the three values should not be treated as interchangeable. Rust refuses to add unrelated numeric types without a conversion, which forces you to choose the result range and sign deliberately. Before adding a cast, ask whether negative values are possible, whether the result can exceed the smaller type, and whether rounding matters.