Structs

A struct groups related values of possibly different types under one name — C's building block for modeling real-world things, without any of the classes or methods of an object-oriented language.

Syntax

struct Point {
    int x;
    int y;
};

Example

struct Point p = {3, 4};
printf("%d, %d\n", p.x, p.y);

p.x = 10;
printf("%d\n", p.x);

Expected output

3, 4
10

A struct is passed to a function by value by default (the whole thing is copied) — pass a pointer to it instead when the function needs to modify the original, or to avoid copying a large struct:

void movePoint(struct Point *p, int dx, int dy) {
    p->x += dx;   // -> is shorthand for (*p).x
    p->y += dy;
}

Common mistakes

• Writing p.x when p is actually a pointer to a struct (struct Point *p) — that needs p->x (or the equivalent but clunkier (*p).x).

Practice

Define a struct Rectangle with width and height, and write a function that returns its area.

struct Rectangle {
    int width;
    int height;
};

int area(struct Rectangle r) {
    return r.width * r.height;
}