A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in D has a specific type, which 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 the variable.
The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because D is case-sensitive. Based on the basic types explained in previous chapter, there will be the following basic variable types: