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Generate random number
Source position: systemh.inc line 794
function Random( 
l: LongInt 
):LongInt; 
l: Int64 
):Int64; 
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. 
None.

Initialize random number generator 
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.