C Playground

A starter program to experiment with. Edit it here, press Copy, paste it into a file called main.c, and compile and run it with cc -std=c17 -Wall -Wextra main.c -o main && ./main. Lesson 2 shows how to install a compiler.

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

typedef struct {
    char name[24];
    double price;
    int quantity;
} Item;

static double line_total(const Item *item) {
    return item->price * item->quantity;
}

static int by_total_desc(const void *a, const void *b) {
    double x = line_total(a), y = line_total(b);
    return (x < y) - (x > y);
}

int main(void) {
    Item basket[] = {
        { "Notebook", 3.50, 4 },
        { "Pen", 1.20, 10 },
        { "Backpack", 39.90, 1 },
    };
    size_t count = sizeof basket / sizeof basket[0];

    qsort(basket, count, sizeof basket[0], by_total_desc);

    double total = 0;
    for (size_t i = 0; i < count; i++) {
        printf("%-10s %3d x %6.2f = %7.2f\n", basket[i].name, basket[i].quantity,
               basket[i].price, line_total(&basket[i]));
        total += line_total(&basket[i]);
    }
    printf("Total: %.2f\n", total);
    return 0;
}

Edit the code, copy it into main.c, then compile and run it with cc -std=c17 -Wall main.c -o main && ./main. How to set up a C compiler

Output

Backpack     1 x  39.90 =   39.90
Notebook     4 x   3.50 =   14.00
Pen         10 x   1.20 =   12.00
Total: 65.90

Ideas to try

Apply a 10% discount when the total is over 50 (lesson 16).
Read the items from a CSV file instead of hard-coding them (lesson 47).
Let the user add items from the keyboard, growing the basket with realloc (lessons 15 and 37).
Store prices as whole cents to avoid rounding errors (lesson 9).
Compile with -fsanitize=address,undefined and try introducing an off-by-one bug in the loop (lesson 38).

Compiling without installing anything

Online compilers such as Compiler Explorer (godbolt.org) can compile and run C in your browser — useful for quick experiments. Choose a recent GCC or Clang and add -std=c17 -Wall -Wextra to the compiler options.

PreviousProject: Gradebook NextExercises