Structs and Pointers: the Arrow ->

Passing a big struct to a function copies all of it, and the function can't change the original. So we usually pass a pointer to the struct instead.

With a pointer, you reach a field with the arrow -> instead of the dot:

#include <stdio.h>

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

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

void show(Account *acc) {
    printf("%s has %d\n", acc->owner, acc->balance);
}

int main() {
    Account a;
    sprintf(a.owner, "Ravi");
    a.balance = 100;
    deposit(&a, 50);
    deposit(&a, 25);
    show(&a);
    return 0;
}

Output

Ravi has 175

• Account *acc: the function receives the address of an account.
• acc->balance: "the balance of the account that acc points to".
• deposit(&a, 50): we pass the address, so the real account changes.

Remember: Use the dot . with a struct variable, and the arrow -> with a pointer to a struct. (acc->balance is short for (*acc).balance.)

Think of it like this: The arrow looks like it is pointing: "follow this pointer, then take the field".