Variables and types

2 min read 4 runnable examples Quiz included

C++ is statically typed: every variable has a type, fixed when it's declared.

Type	Holds	Example
`int`	whole numbers	`int lives = 3;`
`double`	decimal numbers	`double price = 19.99;`
`char`	one character	`char grade = 'A';`
`bool`	`true` or `false`	`bool done = false;`

C++

#include <iostream>
using namespace std;

int main() {
    int lives = 3;
    double price = 19.99;
    char grade = 'A';
    bool gameOver = false;

    cout << "Lives: " << lives << endl;
    cout << "Price: " << price << endl;
    cout << "Grade: " << grade << endl;
    cout << "Game over? " << gameOver << endl;
    return 0;
}

cout prints false as 0 and true as 1.

Changing values

C++

#include <iostream>
using namespace std;

int main() {
    int score = 10;
    score += 5;     // 15
    score *= 2;     // 30
    score--;        // 29
    cout << score << endl;
    return 0;
}

Integer and decimal division

C++

#include <iostream>
using namespace std;

int main() {
    int a = 7, b = 2;
    cout << a / b << endl;              // 3: integer division
    cout << a % b << endl;              // 1: remainder
    cout << (double)a / b << endl;      // 3.5
    cout << 7.0 / 2 << endl;            // 3.5
    return 0;
}

Constants

C++

#include <iostream>
using namespace std;

int main() {
    const double PI = 3.14159;
    const int DAYS_IN_WEEK = 7;
    cout << "Circle area (r=3): " << PI * 3 * 3 << endl;
    cout << "Hours in a week: " << DAYS_IN_WEEK * 24 << endl;
    return 0;
}

Constants are conventionally written in UPPER_CASE.

auto

Modern C++ can work out a variable's type from its value:

C++

auto count = 10;       // int
auto ratio = 0.75;     // double
auto letter = 'x';     // char

auto is handy with long type names; for simple variables, writing the type is clearer.

Finished this lesson?Mark it complete to earn +20 XP and move your progress on.