Arithmetic

C++ can calculate. The basic arithmetic operators (symbols for operations) are:

• + addition
• - subtraction
• * multiplication (an asterisk, because there's no × on the keyboard)
• / division (a slash instead of ÷)
• % the remainder after division, which you'll see in the next exercise

You can calculate with numbers and with variables. You can store the result in a variable, or print it straight away:

int pencilPrice = 2;
int pencils = 6;
int cost = pencilPrice * pencils;
std::cout << "Pencils: " << cost << " EUR\n";
std::cout << "Change from 20: " << 20 - cost << " EUR\n";

This prints:

Pencils: 12 EUR
Change from 20: 8 EUR

As in math, multiplication and division are done before addition and subtraction. Operations with the same priority are done from left to right. If you want a different order, use parentheses:

std::cout << 2 + 3 * 4 << "\n";
std::cout << (2 + 3) * 4 << "\n";

This prints:

14
20

In the first line, 3 * 4 is calculated first, which is 12, and only then 2 + 12. In the second line, the parentheses come first.

A typical mistake is to forget the parentheses. This doesn't calculate the average of two test scores:

int first = 2;
int second = 4;
std::cout << first + second / 2 << "\n";

The program prints 4, because only the second score is divided by two: 2 + 4 / 2 is 2 + 2. The right way is (first + second) / 2, which gives 3.

More things to watch out for:

• You always have to write the multiplication. 2(a + b) ends with the error called object type 'int' is not a function or function pointer; write 2 * (a + b).
• Anything in quotes is text, and it isn't calculated: std::cout << "2 + 3"; prints 2 + 3, not 5.
• Spaces around operators don't change the result. We write them because they make the code easier to read.