Structs and Pointers

Structs and Pointers

Passing structs by pointer is more efficient than copying them, and allows functions to modify the original struct.

Pointer to Struct

struct Point {
    int x;
    int y;
};

struct Point p = {10, 20};
struct Point *pp = &p;

Engineering schematics passed by reference: Geordi doesn't carry the whole warp core to show you -- he hands you a pointer to the diagram.

The Arrow Operator

Use -> to access members through a pointer (equivalent to (*pp).x):

printf("%d\n", pp->x);    // 10
printf("%d\n", pp->y);    // 20
pp->x = 99;               // modify through pointer

Modifying Structs in Functions

void move(struct Point *p, int dx, int dy) {
    p->x += dx;
    p->y += dy;
}

int main() {
    struct Point p = {0, 0};
    move(&p, 5, 3);
    printf("(%d, %d)\n", p.x, p.y);  // (5, 3)
}

Arrays of Structs

struct Point points[3] = {{1, 2}, {3, 4}, {5, 6}};
for (int i = 0; i < 3; i++) {
    printf("(%d, %d)\n", points[i].x, points[i].y);
}

Your Task

Define a struct Counter with an int value field. Write two functions:

• void increment(struct Counter *c) -- increases value by 1
• void add(struct Counter *c, int n) -- increases value by n

Start with a counter at 0, increment it 3 times, then add 10. Print the final value.