(1) Any value passed to a program by the user or by another program in order to customize the program for a particular purpose. A parameter may be anything; for example, a file name, a coordinate, a range of values, a money amount or a code of some kind. Parameters may be required as in parameter-driven software (see below) or they may be optional. Parameters are often entered as a series of values following the program name when the program is loaded.

A DOS switch is a parameter. For example, in the DOS Dir command dir /p the DOS switch /p (pause after every screenful) is a parameter.

(2) In programming, a value passed to a subroutine or function for processing. Programming today's graphical applications with languages such as C, C++ and Pascal requires knowledge of hundreds, if not thousands, of parameters.

In the following C function, which creates the text window for the Windows version of this database, there are 11 parameters passed to the CreateWindow routine. Some of them call yet other functions for necessary information. In order to call this routine in a program, the programmer must decide what the values are for every parameter.

 hWndText = CreateWindow    (
      "TextWClass",
       NULL,
       WS_CHILD|WS_BORDER|WS_VSCROLL|WS_TABSTOP,
       xChar*23+GetSystemMetrics(SM_CXVSCROLL)+8,
       yChar*4,
       Rect.right-Rect.left+1-xChar*23
          -2*GetSystemMetrics(SM_CXVSCROLL)+5,
       yChar*(Lines+1)+2,
       hWnd,
       IDC_TEXTLIST,
       (HANDLE)hInstance,
       NULL                 ) ;