Variables & Data Types

Variables are essentially labeled containers that store data in your computer's memory. Because C++ is a statically-typed language, you must tell the compiler exactly what kind of data a variable will hold before you use it. This allows the computer to reserve the correct amount of space in memory.

1. Common Data Types

Here are the primary types you'll use 90% of the time:

Type DescriptionSize (Typical)Example

intIntegers (whole numbers)4 bytesint age = 25;

doubleFloating-point (decimals)8 bytesdouble price = 19.99;

charSingle characters1 bytechar grade = 'A';

stringSequence of textVariablestring name = "Gemini";

boolBoolean (true/false)1 bytebool isCoding = true;

2. Declaration vs. Initialization

• Declaration: Telling the compiler the name and type (e.g., int score;).

• Initialization: Giving that variable its first value (e.g., score = 100;).

• You can do both at once: int score = 100;.

#include <iostream>
#include <string> // Required to use the string data type
using namespace std;

int main() {
    // 1. Variable definitions
    string playerName = "Alex";
    int health = 100;
    double shieldEnergy = 75.5;
    char rank = 'S';
    bool isGameOver = false;

    // 2. Performing an operation
    int damage = 20;
    health = health - damage; // Updating the variable

    // 3. Outputting the data
    cout << "Player: " << playerName << endl;
    cout << "Rank: " << rank << endl;
    cout << "Health: " << health << "%" << endl;
    cout << "Shield: " << shieldEnergy << " units" << endl;
    
    // Boolean outputs 1 for true, 0 for false
    cout << "Game Over? " << isGameOver << endl; 

    return 0;
}

Key Rules for Naming (Identifiers)

• Names can contain letters, digits, and underscores.

• They must begin with a letter or an underscore (_).

• C++ is case-sensitive (myVar and myvar are different).

• You cannot use "Keywords" (like int, return, or class) as names.