Identifiers

4. Variables

All the variables we have used so far were named using letters a, b, x, y, z, A. However, variable names need not consist of a single letter. In fact, it is recommended to use names that describe what variables stand for. In C++, names can be composed of lower case and upper case letters of the English alphabet, numerals, and the symbol '_', called the underscore. In addition, no name may begin with a digit, and no spaces are allowed: that is, a name must be a single word.

Here are a few examples:

Valid Name	Invalid Name
`second_factor`	`second factor`
`row5`	`5row`
`areaOfTriangle`	`area of triangle`
`NoSpaces`	`No Spaces`
`omega`	`Ω`
`__icecream`	`ice-cream`
`num_of_elements`	`num of elements`
`PI`	`π`
`l33t`	`1337`

Another important thing to remember is that C++ distinguishes lowercase and uppercase letters. That is why a and A are two different names. Also, friday and Friday are two different names. In other words, the C++ language is case-sensitive.

Since names in C++ are used to uniquely identify a variable or some other thing, they are more properly called identifiers.