C Structures

C structures, written with the struct keyword, group variables of different types under one name. A struct is perfect for representing a real thing, such as a student with a name, age and GPA.

Defining and Using a Struct

#include <stdio.h>

struct Student {
    char name[30];
    int age;
    double gpa;
};

int main(void) {
    struct Student s = {"Ayesha", 21, 3.8};
    printf("%s, %d, GPA %.1f\n", s.name, s.age, s.gpa);
    s.age = 22;
    printf("New age: %d\n", s.age);
    return 0;
}

Ayesha, 21, GPA 3.8
New age: 22

typedef and Designated Initializers

typedef gives the struct a shorter name so you can skip the struct keyword. Designated initializers set members by name.

#include <stdio.h>

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

int main(void) {
    Point p = {.y = 8, .x = 3};
    printf("(%d, %d)\n", p.x, p.y);
    return 0;
}

(3, 8)

Pointers to Structs and the Arrow Operator

When you have a pointer to a struct, use -> to access members. p->x is short for (*p).x. Passing a pointer avoids copying a large struct and lets the function modify it.

#include <stdio.h>

typedef struct {
    char owner[20];
    double balance;
} Account;

void deposit(Account *acc, double amount) {
    acc->balance += amount;
}

int main(void) {
    Account a = {"Bilal", 100.0};
    deposit(&a, 50.0);
    printf("%s: %.2f\n", a.owner, a.balance);
    return 0;
}

Bilal: 150.00

Arrays of Structures

#include <stdio.h>

typedef struct {
    const char *name;
    int qty;
} Item;

int main(void) {
    Item cart[] = {{"Rice", 2}, {"Tea", 1}, {"Oil", 3}};
    for (int i = 0; i < 3; i++) {
        printf("%-5s x%d\n", cart[i].name, cart[i].qty);
    }
    return 0;
}

Rice  x2
Tea   x1
Oil   x3

Frequently asked questions

What is the difference between . and -> in C?

Use the dot operator with a struct variable (s.age) and the arrow operator with a pointer to a struct (p->age).

Why use typedef with struct in C?

typedef creates an alias so you can write Point p instead of struct Point p. It makes code shorter and easier to read.

Can a struct contain another struct in C?

Yes. Members can be any type, including other structs, arrays and pointers. Access nested members with chained dots, like order.customer.name.