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Adding products

Write the function that adds products to the cart.

The cart_add function

In this lesson we'll write the cart_add function. It adds a new item to the cart and increments cart_size.

void cart_add(const char *name, double price, int qty) {
    if (cart_size >= MAX_ITEMS) return;
    strcpy(cart[cart_size].name, name);
    cart[cart_size].price = price;
    cart[cart_size].qty = qty;
    cart_size++;
}

strcpy copies the string; cart_size points to the next free slot. If the cart is full, we return early. This safety check prevents overflow.

Copying strings with strcpy

In C you can't assign strings with =; you must use strcpy. strcpy copies a string into a destination array character by character.

char name[32];
strcpy(name, "Apple");  // name is now "Apple"

That's why we use strcpy(cart[cart_size].name, name) inside cart_add. It's declared in the string.h header. To prevent overflow, strncpy can be preferred.

Practice Add two items

Write the cart_add function: void cart_add(const char *name, double price, int qty). If the cart is full (cart_size >= MAX_ITEMS) return early. Copy the name with strcpy, set price and qty, then cart_size++. main already adds two items; just complete the function. Expected output: 2 items added.

Starter code

main.c
#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;

// Write the cart_add function here

int main(void) {
    cart_add("Apple", 2.50, 3);
    cart_add("Bread", 5.00, 1);
    printf("%d items added\n", cart_size);
    return 0;
}

Sample solution

main.c
#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;

void cart_add(const char *name, double price, int qty) {
    if (cart_size >= MAX_ITEMS) return;
    strcpy(cart[cart_size].name, name);
    cart[cart_size].price = price;
    cart[cart_size].qty = qty;
    cart_size++;
}

int main(void) {
    cart_add("Apple", 2.50, 3);
    cart_add("Bread", 5.00, 1);
    printf("%d items added\n", cart_size);
    return 0;
}

Expected output

2 items added

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Increment cart_size

Question 
void cart_add(const char *name, double price, int qty) {
    if (cart_size >= MAX_ITEMS) return;
    strcpy(cart[cart_size].name, name);
    cart[cart_size].price = price;
    cart[cart_size].qty = qty;
    ____;
}
Answer 
void cart_add(const char *name, double price, int qty) {
    if (cart_size >= MAX_ITEMS) return;
    strcpy(cart[cart_size].name, name);
    cart[cart_size].price = price;
    cart[cart_size].qty = qty;
    cart_size++;
}

Explanation: cart_size++ moves to the next free slot.

2 What's cart_size after cart_add?

main.c
cart_add("Apple", 2.50, 3);
cart_add("Bread", 5.00, 1);
  • 0
  • 2 Correct answer
  • 1
  • MAX_ITEMS

Explanation: After two adds cart_size = 2.

3 Match the add pieces

Term Meaning
strcpy Copies a string
cart_size++ Increments count
MAX_ITEMS Upper bound
void cart_add Function signature

All lessons in Beginner

1 C basics

  1. What is C?
  2. Your first program
  3. Compile and run
  4. Comments
  5. printf and escapes
  6. Summary - C basics

2 Variables

  1. Declaring variables
  2. Variable assignment
  3. const
  4. Variable scope
  5. typedef
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. char
  4. sizeof
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Menu loop
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 I/O

  1. printf formatting
  2. scanf
  3. Multiple inputs
  4. getchar and putchar
  5. puts and fputs
  6. Summary - I/O

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. break and continue
  5. Nested loops
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. Declaring arrays
  2. Array access
  3. Array size
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 Strings

  1. String basics
  2. String literals
  3. strlen
  4. strcpy and strcat
  5. strcmp
  6. Summary - Strings

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function prototypes
  5. Recursion
  6. Summary - Functions

13 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. NULL
  5. Pointer arithmetic
  6. Summary - Pointer basics

14 Arrays and pointers

  1. Array name as pointer
  2. Pointer to array
  3. Passing arrays to functions
  4. Pointer loop
  5. Multidim array pointer
  6. Summary - Arrays and pointers

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 String functions

  1. strchr
  2. strstr
  3. strtok
  4. sprintf
  5. sscanf
  6. Summary - String functions

17 Structs

  1. Defining structs
  2. Using structs
  3. typedef struct
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Memory and stack

  1. Stack and heap
  2. Automatic storage
  3. malloc
  4. free
  5. calloc and realloc
  6. Summary - Memory and stack

19 Preprocessor

  1. #define
  2. #include
  3. Conditional compilation
  4. Macro functions
  5. Header files
  6. Summary - Preprocessor

20 Beginner final

  1. Project design
  2. Data model
  3. Functions
  4. Memory management
  5. Putting it together