Data Types and Variables

Most values in a computer program have a type. The type tells C++ what the value represents and what operations make sense for it.

Common C++ types include:

• Integer types: short, int, long, and long long
• Floating-point types: float, double, and long double
• Character and Boolean types: char and bool
• Compound types: arrays, pointers, references, enums, classes, and string

Variables

A variable is a named storage location. C++ is statically typed, so every variable declaration states what kind of data the variable can store.

For example, int num = 10; gives a type, name, and initial value, followed by a semicolon.

int num = 10;
cout << num << endl;      // 10

double salary = 8232.56;
cout << salary << endl;   // 8232.56

Here, num is declared as int, while salary is declared as double. C++ checks later assignments against those types.

Naming variables

Good variable names are clear and valid:

• Use letters, digits, and underscores, but do not start with a digit.
• Do not use C++ reserved keywords.
• Prefer meaningful English words.

Names like age, student_name, and total_score are easier to read than a or x1.

C++ keywords

Keywords are reserved by C++ and cannot be used as ordinary variable names.

Common keywords include:

• bool, char, int, and double
• if, else, switch, and case
• for, while, break, and continue
• class, struct, public, and private
• try, catch, throw, and namespace

Using a keyword as a variable name would make C++ unable to tell whether you mean a language feature or an ordinary value.