4. Arithmetic

4.1 Introduction to Arithmetic

Computers are useful because it can do calculations very quickly. C allows us to perform some arithmetic operations, as well as some logical operations (the next topic!)

We'll introduce some new symbols - addition, subtraction, multiplication and 'division'!

4.2 Multiplication example

Let's buy some pizza.

#include <stdio.h>

int main () {
    int pizzas = 10; // Create a variable
    int cost = pizzas * 8;

    // print out the number and price of pizzas
    printf("%d pizzas cost %d.\n", pizzas, cost);
    return 0;
}

• The cost of the pizzas is 8 dollars, and we purchase 10 pizzas.
  • We calculate the cost in this line: cost = pizzas * 8
• To print out both numbers, we add another placeholder %d, and fill it in with another argument, cost. Look carefully at the location of the quotes and commas.

4.3 Division and Remainder example

Let's split our pizza and share some slices!

#include <stdio.h>

int main () {
    // We have 17 slices of pizza to share between 4 people.
    int slices = 17;
    int people = 4;

    // print out how many slices per person
    printf("Each person gets %d slices.\n", slices / people);
    // print out the remainder
    printf("There will be %d slices left.\n", slices % people);
    return 0;
}

• Note that wherever you can place a number of variable, you can place the arithmetic equation. Here, we don't create new variables (e.g. there's no slicesPerPerson and slicesLeft - we just let printf calculate it before printing.

4.3 Exercises

• There are exercises in the grouped exercises.