Cart design

Design the structure and array for the shopping cart.

Project: Shopping cart

In this 5-lesson project you'll build a shopping cart. Each lesson adds one piece, and by the final lesson you'll have a complete app.

You'll use what you learned before:

data structure with struct
int and double variables
formatted output with printf
loops with for

You'll also learn cart_add, cart_subtotal and cart_list functions. Ready? Let's start.

The CartItem struct

We'll define a struct CartItem for a cart entry. Each item has a name, a price and a quantity. The cart is an array of this struct.

struct CartItem {
    char name[32];
    double price;
    int qty;
};

struct CartItem cart[MAX_ITEMS];
int cart_size = 0;

Here MAX_ITEMS is the maximum items the cart can hold. cart_size tracks the current count. As you add to the cart, cart_size grows.

Exercise Write the cart skeleton

Write a C program. Define the struct CartItem (with char name[32]; double price; int qty;). Define struct CartItem cart[MAX_ITEMS]; and int cart_size = 0;. In main print printf("Cart ready\n"); and printf("%d items\n", cart_size);. Put #include <stdio.h> and #include <string.h> at the top. You can add #define MAX_ITEMS 10.

Show example solution

#include <stdio.h>
#include <string.h>

#define MAX_ITEMS 10

struct CartItem {
    char name[32];
    double price;
    int qty;
};

struct CartItem cart[MAX_ITEMS];
int cart_size = 0;

int main(void) {
    printf("Cart ready\n");
    printf("%d items\n", cart_size);
    return 0;
}

Test yourself

What does a cart need first?
```
struct CartItem { ... };
struct CartItem cart[MAX_ITEMS];
```
- A struct and an array
- A database
- A file
- A pointer
Show answer

A struct and an array — A cart starts with a struct and an array.

Complete the struct definition

struct CartItem {
    char name[32];
    double price;
    int ____;
};

Show answer

struct CartItem {
    char name[32];
    double price;
    int qty;
};

Match the cart pieces

struct CartItem

Item struct
cart[MAX_ITEMS]

Cart array
cart_size

Item count
MAX_ITEMS

Upper bound

Next lesson: Adding products

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