Arrays of Structures and Pointers to Structures

Big idea

An array of structs holds many records. A pointer to a struct reaches members with the arrow operator ->.

Arrays of structs

One struct is one record; an array of them is a table:

#include <stdio.h>

struct Student {
    char name[20];
    int mark;
};

int main(void) {
    struct Student cls[4] = {
        {"Asha", 88},
        {"Ben", 72},
        {"Chen", 95},
        {"Dev", 81},
    };
    int top = 0;
    for (int i = 1; i < 4; i++) {
        if (cls[i].mark > cls[top].mark) {
            top = i;
        }
    }
    printf("Top: %s with %d\n", cls[top].name, cls[top].mark);
    return 0;
}

output
Top: Chen with 95

cls[i].mark reads left to right: element i of the array, then its mark member.

Watch it

Pointers to structs and ->

With a pointer p to a struct, you could write (*p).mark — follow the pointer, then take the member. The brackets are needed because . binds tighter than *. C gives you a shortcut:

p->mark      // exactly the same as (*p).mark

Changing a struct in a function

Passing a struct copies it, so a function that should change a record takes a pointer:

#include <stdio.h>

struct Person {
    char name[20];
    int age;
};

void birthday(struct Person p) {
    p.age++;
}

int main(void) {
    struct Person me = {"Riya", 19};
    birthday(me);
    printf("%s is %d\n", me.name, me.age);
    return 0;
}

output
Riya is 20

Change the parameter to struct Person *p, use p->age++, and call birthday(&me).

Think of it like

A filing cabinet of identical forms (the array). Handing a colleague the drawer number (a pointer) lets them update the real form, instead of a photocopy.

🕷️ Spidey-sense: My rogues' gallery is an array of struct Villains. When Doc Ock upgrades his arms, I update villains[3].threat_level — or ock->threat_level when I've got a pointer to his file.

Key terms

• Array of structs — Many records of the same shape.
• -> (arrow operator) — Member access through a pointer: p->x means (*p).x.