Structs and typedef: . vs ->

Grouping related data

• A struct groups several values into one thing. A point has an x and a y; a rectangle has a width and a height.
• Each value inside is called a member (or field). They can have different types.
• Structs let you pass one tidy thing around instead of many loose variables.

struct and typedef

• You define the shape once: struct { int x; int y; } has two int members.
• typedef gives that shape a short name. After typedef struct { int x; int y; } Point;, you can write Point p;.
• In these tasks, the typedef is already written for you in the starter.

Member access with .

• For a struct value, use a dot: p.x is the x member of p.
• You read it (int a = p.x;) and write it (p.y = 5;) just like a normal variable.
• A function can build a struct, fill its members, and return the whole thing.

Through a pointer with ->

• When you have a pointer to a struct, use an arrow: p->x means "the x of what p points to".
• p->x is just shorthand for (*p).x. The arrow is easier to read.
• Passing a Point * lets a function change the caller's struct (like pass-by-pointer for one value).

#include <stdio.h>

typedef struct {
    int x;
    int y;
} Point;

int main(void) {
    Point p = {3, 4};
    Point *ptr = &p;
    ptr->x = 10;                    // changes p.x through the pointer
    printf("%d %d\n", p.x, p.y);    // 10 4
    return 0;
}

Common mistakes

• Use . on a struct value and -> on a struct pointer.
• typedef lets you drop the word struct when declaring.

Now you try

• Use . on a struct value, and -> when you have a pointer to a struct.
• The typedef is given in each starter. Do not write a main — the checker provides one.