Variables and Initialization

A variable is a named piece of memory with a type. In C++, you declare it once and the compiler enforces the type forever:

int score = 0;            // whole numbers
double price = 19.99;     // floating point
char grade = 'A';         // a single character (single quotes!)
bool passed = true;       // true or false
std::string name = "Ha";  // text (double quotes) — needs #include <string>

Declaration vs initialization vs assignment

• Declaration creates the variable: int x;
• Initialization gives it its first value — do it on the same line, always.
• Assignment replaces the value later: x = 5;

An uninitialized variable contains garbage. Not "zero", not "empty" — garbage: whatever bits were already in that memory. Reading it is undefined behavior.

Brace initialization — the modern default

int width{10};          // preferred modern form
int y = 3.7;            // compiles: y becomes 3 — silently!
int z{3.7};             // error: narrowing conversion — compiler catches it

Braces refuse lossy conversions. That is why this course writes {} for new variables: the compiler becomes your safety net.

auto — say the type once

auto count = 10;        // int — the compiler deduces it from the initializer
auto ratio = 0.5;       // double
auto title = std::string{"Report"};

auto is not a "dynamic type" (types are still fixed at compile time); it just avoids repeating them. Rule of thumb in this course: use explicit types for simple values, auto when the type is obvious from the right-hand side. (More in lesson 2C.)

Names matter

int x2tmp1; compiles; int pending_items; communicates. Modern C++ style: snake_case for variables and functions, PascalCase for types you will meet in module 10.

Practice next: declare, initialize, and compute — the compiler will grade your types.