Struct Basics

Defining and declaring

struct Point {          // defines a new TYPE
    int x;
    int y;
};

struct Point p = {3, 4};        // positional initializer
struct Point q = {.x = 3, .y = 4};  // designated (clearer, order-free)

The struct keyword is part of the type name. Members are accessed with the dot: p.x, p.y.

Assignment copies the whole thing

struct Point a = {1, 2};
struct Point b = a;     // b gets its OWN copy of both members
b.x = 99;               // a.x is still 1

Arrays copy element-by-element only when you write the loop; structs copy in one assignment. That makes them natural value objects.

Nested structs

struct Rect {
    struct Point topleft;
    struct Point size;
};
struct Rect r = {{0, 0}, {10, 5}};
printf("%d\n", r.size.y);   // 5 — dots chain

Arrays of structs

struct Point pts[3] = {{1, 1}, {2, 2}, {3, 3}};
printf("%d\n", pts[1].x);   // 2 — index first, then member