Understand how to declare and use variables of different data types.
In C++, a variable is a name given to a memory location. It is the basic unit of storage in a program. Before you can use a variable, you must declare it, which involves specifying its type and name. The type determines the size and layout of the variable's memory, the range of values that can be stored within that memory, and the set of operations that can be applied to it. For example, `int age;` declares a variable named `age` of type `integer`. C++ has several built-in (primitive) data types: `int` for whole numbers (e.g., 10, -5), `double` and `float` for numbers with decimal points (e.g., 3.14, -0.05), `char` for single characters (e.g., 'a', '$'), and `bool` for logical values (`true` or `false`). You can also use type modifiers like `short`, `long`, `signed`, and `unsigned` to alter the storage size or range of these basic types. For instance, `unsigned int` can only hold non-negative values, but its maximum value is roughly twice that of a `signed int`. Initialization is the process of assigning an initial value to a variable at the time of its declaration, like `int score = 0;`. It's a good practice to always initialize your variables to avoid using them with indeterminate 'garbage' values, which can lead to unpredictable program behavior.