A variable is a named piece of memory that you define.
Each variable only stores data of a particular type.
Every variable has a type that defines the kind of data it can store.
Each fundamental type is identified by a unique type name that is a keyword.
Keywords are reserved words in C++.
You do have to follow a few simple C++ naming rules:
The only characters you can use in names are alphabetic characters, numeric digits, and the underscore (_) character.
The first character in a name cannot be a numeric digit.
Uppercase characters are considered distinct from lowercase characters.
You can't use a C++ keyword for a name.
Here are some valid and invalid C++ names:
int myvalue; // valid int MyValue; // valid and distinct int MYVALUE; // valid and even more distinct Int three; // invalid -- has to be int, not Int int my_value3 // valid int _Myvalue3; // valid but reserved -- starts with underscore
To form a name from two or more words, the usual practice is to separate the words with an underscore character, as in my_onions, or to capitalize the initial character of each word after the first, as in myEyeColor.
C++ uses the const keyword to declare constant value.
const int Months = 12; // Months is symbolic constant for 12
The general form for creating a constant is this:
const type name = value;
Note that you initialize a const in the declaration.