Variables are references that stand in for a value that is contained at a certain memory address.
Variables are said to have a value and may have a data type. If a variable has a type, then only values of this type may be assigned to it. Variables do not always have a type.
A value can have many values of many different types: integers (7), ratios (1/2), (approximations of) reals (10.234), complex numbers (4+2i), characters ('a'), strings ("hello"), and much more.
Different languages use different names for their types and may not include any of the above.
Assignment statements[edit source]
An assignment statement is used to set a variable to a new value.
Assignment statements are written as
name := value.
X := 10;
The example set the variable X to the integer value of 10. The assignment statement overwrites the contents of the variable and the previous value is lost.
In some languages, before a variable can be used, it will have to be declared, where the declaration specifies the type.
Ada is the same. The declaration is as follows:
declareX : Integer := 10;
Variables store everything in your program. The purpose of any useful program is to modify variables.