Zig Integer Division

Integer division is division between whole numbers that gives a whole-number result.

The / operator truncates the fraction

Both divisions below have fractions. Both fractions are dropped.

const std = @import("std");

pub fn main() !void {
    const out = std.io.getStdOut().writer();
    try out.print("{d}\n", .{7 / 2});
    try out.print("{d}\n", .{8 / 3});
}

@divTrunc and @rem split a division

@divTrunc gives the whole part. @rem gives the leftover.

const std = @import("std");

pub fn main() !void {
    const out = std.io.getStdOut().writer();
    try out.print("{d}\n", .{@divTrunc(17, 5)});
    try out.print("{d}\n", .{@rem(17, 5)});
}

Negative division truncates toward zero

A negative result drops its fraction too. The remainder keeps the sign of the first number.

const std = @import("std");

pub fn main() !void {
    const out = std.io.getStdOut().writer();
    const a: i32 = -7;
    const b: i32 = 2;
    try out.print("{d}\n", .{a / b});
    try out.print("{d}\n", .{@divTrunc(a, b)});
    try out.print("{d}\n", .{@rem(a, b)});
}

Example

const std = @import("std");

pub fn main() !void {
    const out = std.io.getStdOut().writer();
    const total_minutes = 125;
    const hours = @divTrunc(total_minutes, 60);
    const minutes = @rem(total_minutes, 60);
    try out.print("{d}\n", .{hours});
    try out.print("{d}\n", .{minutes});
}

Key points

Truncation: dropping the fraction part of a result is called truncation.
Use / to divide integers, and Zig truncates the result toward zero.
Builtin: a builtin is a function built into Zig, and its name starts with @.
Use @divTrunc(a, b) to divide with truncation and name the operation clearly.
Use @rem(a, b) to get the remainder left after truncated division.
Negative results: -7 / 2 gives -3, because truncation moves toward zero, not down.

In this example, @divTrunc divides 125 by 60 and gives 2 whole hours. @rem gives the 5 minutes left over. Together they split 125 minutes into 2 hours and 5 minutes.

Note

floor division would round -7 / 2 down to -4, so it gives a different answer from Zig.

Try it Yourself

Edit the code, then press Run.

Running is simulated

const std = @import("std");

pub fn main() !void {
    const out = std.io.getStdOut().writer();
    const total_minutes = 125;
    const hours = @divTrunc(total_minutes, 60);
    const minutes = @rem(total_minutes, 60);
    try out.print("{d}\n", .{hours});
    try out.print("{d}\n", .{minutes});
}

Exercise

What does @rem(19, 6) give?

3 0 1 6