[Overview][Constants][Types][Classes][Procedures and functions][Variables][Index] Reference for unit 'System' (#rtl)

Random

Generate random number

Declaration

Source position: line 0

function Random(

  l: LongInt

):LongInt;

function Random(

  l: Int64

):Int64;

function Random: extended;

Description

Random returns a random number larger or equal to 0 and strictly less than L. If the argument L is omitted, a Real number between 0 and 1 is returned (0 included, 1 excluded).

Remark: The Free Pascal implementation of the Random routine uses the Mersenne Twister to simulate randomness. This implementation has a better statistical distribution than for example a Linear Congruential generator algorithm, but is considerably slower than the latter. If speed is an issue, then alternate random number generators should be considered.

Errors

None.

See also

Randomize

  

Initialize random number generator

Example

Program Example49;

{ Program to demonstrate the Random and Randomize functions. }

Var I,Count,guess : Longint;
    R : Real;

begin
  Randomize; { This way we generate a new sequence every time
               the program is run}
  Count:=0;
  For i:=1 to 1000 do
    If Random>0.5 then inc(Count);
  Writeln ('Generated ',Count,' numbers > 0.5');
  Writeln ('out of 1000 generated numbers.');
  count:=0;
  For i:=1 to 5 do
    begin
    write ('Guess a number between 1 and 5 : ');
    readln(Guess);
    If Guess=Random(5)+1 then inc(count);
    end;
  Writeln ('You guessed ',Count,' out of 5 correct.');
end.

Documentation generated on: Mar 14 2014