Parameters

A parameter is a numerical or other measurable factor forming one of a set that defines a system or sets the conditions of its operation.

A parameter passing is the process of providing a procedure, function or module with values at the point when you call it.

By Value is if a data item is passed by value, a (local) copy of the data is used, which is discarded when the subprogram exits.

By Reference is if a data item is passed by reference, the location (in memory) of the data is used. This means that any changes are retained after the procedure or function has been completed.

For example