In contrast to a variable, a constant represents a fixed, non-changeable value. In programming, the value of the constant should not change through the program flow.
A constant has a unique identifier, a data type and the fixed value from the value system. In programming, the identifier and the data type are agreed by declaration. This refers to the definition of dimensions
, data types and variables. Such a declaration protects the constant from changes. Typical examples of constants are tax rates such as value added tax, the number "e", "pi" or the prefix for capital "K".