Project: A Tiny Bank

Many programs work like this: show a menu, read a command, do it, repeat until the user quits. Here is a tiny bank:

#include <stdio.h>

typedef struct {
    int balance;
    int transactions;
} Account;

void deposit(Account *acc, int amount) {
    acc->balance += amount;
    acc->transactions++;
    printf("Deposited %d. Balance: %d\n", amount, acc->balance);
}

void withdraw(Account *acc, int amount) {
    if (amount > acc->balance) {
        printf("Not enough money! Balance: %d\n", acc->balance);
        return;
    }
    acc->balance -= amount;
    acc->transactions++;
    printf("Withdrew %d. Balance: %d\n", amount, acc->balance);
}

int main() {
    Account acc;
    acc.balance = 0;
    acc.transactions = 0;

    char command;
    int amount;
    scanf(" %c", &command);
    while (command != 'q') {
        if (command == 'd') {
            scanf("%d", &amount);
            deposit(&acc, amount);
        } else if (command == 'w') {
            scanf("%d", &amount);
            withdraw(&acc, amount);
        } else if (command == 'b') {
            printf("Balance: %d\n", acc.balance);
        } else {
            printf("Unknown command %c\n", command);
        }
        scanf(" %c", &command);
    }
    printf("Goodbye! %d transactions.\n", acc.transactions);
    return 0;
}

Input (what the user types)

d 100
w 30
w 500
b
x
q

Output

Deposited 100. Balance: 100
Withdrew 30. Balance: 70
Not enough money! Balance: 70
Balance: 70
Unknown command x
Goodbye! 2 transactions.

What to notice

• The loop keeps going until the user types q.
• " %c" (with a space) skips the Enter keys between commands.
• The functions get a pointer to the account, so they change the real one.
• withdraw uses an early return to refuse a withdrawal that is too big.

Tip: Ideas to extend it: add an interest command, or keep several accounts in an array.