Declaring variables

Learn to declare variables of type int, double, char, bool and float.

Declaring variables

A variable is a box that holds a value by name. In C++ you declare a variable by writing its type, then its name, then an optional initial value: int score = 90;.

Common types: int (integer), double (floating-point), float (single-precision decimal), char (single character) and bool (true/false).

A variable name must start with a letter or underscore and contain no spaces. English letters are recommended for portability.

Initialization

Giving a variable a value when it is declared is called initialization. int x = 5; sets x to 5. int x; leaves x uninitialized; reading it before assigning causes undefined behavior.

Three initialization forms are common in C++:

int x = 5; — copy initialization
int x{5}; — brace initialization (prevents narrowing)
int x(5); — parenthesis initialization

Initialization adds safety and predictability; always assign a value before reading a variable.

Exercise Declare four types and print

Inside main, declare an int, a double, a char and a bool variable with the values 90, 19.99, 'A' and true respectively. Print each on its own std::cout line using std::endl.

Show example solution

#include <iostream>

int main() {
    // Declare an int, a double, a char and a bool
    int score = 90;
    double price = 19.99;
    char grade = 'A';
    bool active = true;
    // Print each with std::cout
    std::cout << score << std::endl;
    std::cout << price << std::endl;
    std::cout << grade << std::endl;
    std::cout << active << std::endl;
    return 0;
}

Test yourself

Which is a valid variable declaration?
- int 2count = 5;
- int count = 5;
- int count = ;
- int = 5;
Show answer

int count = 5; — int count = 5; is a valid declaration.

Floating-point variable

____ price = 19.99;

Show answer

double price = 19.99;

Match types with examples

int

90
double

19.99
char

'A'
bool

true

Next lesson: auto

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