factorial.pas

program factorial;
Uses sysutils;

const
   MAXFACT  = 20;
   VERSION  = 0.1;
   COPYDATE = 'January 3, 2019';
   WEBSITE  = 'http://mcsuper5.freeshell.org/programs.html';

var
   num, f  : Int64;
   HELP	   : Boolean;
   QUIET   : Boolean;
   VERBOSE : Boolean;
   NUMSET  : Boolean;
   code	   : word;
   i	   : Integer;

function fact(x	:  Int64): Int64;
begin
   if x=0
      then
         fact:= 1
      else
	 fact := x * fact(x-1);
end;

procedure Copyright;
begin
   writeln('factorial version ', VERSION:3:1,
	   '  Copyright ', COPYDATE, '  Michael J. Chappell');
   writeln('The latest version can be found at: ',WEBSITE);
   writeln;
end;

procedure Usage;
begin
   writeln('Factorial - Prints the factorial of an integer between ',
	   '1 and ', MAXFACT, '.');
   writeln('Michael J. Chappell   ', COPYDATE);
   writeln;
   writeln('Usage is:');
   writeln;
   writeln('    factorial [-h][-q][-v][n]');
   writeln;
   writeln('-h  Prints this help message.');
   writeln('-q  Quiet.  Prints the result only.');
   writeln('-v  Verbose. Includes copyright information.');
   writeln;
   writeln('Where ''n'' is an integer between 1 and ', MAXFACT, '.');
   writeln('You will be prompted for ''n'' if it is not provided.');
   writeln;
   Copyright;
end;

procedure printResult(n, f : Int64; QUIET, VERBOSE : Boolean);
begin
   if VERBOSE then Copyright;
   if QUIET then
      writeln(f)
   else
      writeln(n:2,'! = ',f);
end;

begin
   QUIET := False;
   VERBOSE := False;
   NUMSET := False;
   HELP := False;
   for i:=0 to argc-1 do
   begin
      if AnsiCompareStr(argv[i],'-q')=0 then QUIET := TRUE;
      if AnsiCompareStr(argv[i],'-v')=0 then VERBOSE := TRUE;
      if AnsiCompareStr(argv[i],'-h')=0 then HELP := True;
      val(argv[i],num,code);
      if code=0 then
      begin
	 NUMSET := True;
      end;
   end; { for }
   if (NOT NUMSET) and (NOT HELP) then
   begin
      write('For which number would you like to find the factorial? (1-20) ');
      readln(num);
   end; { if }
   if (num>MAXFACT) or (num<1) then HELP := TRUE;
   if HELP then
      Usage
   else
      printResult(num, fact(num), QUIET, VERBOSE);
end.
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Friday, 18 July 2025 Michael J. Chappell Contact me at: mcsuper5@freeshell.org
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factorial.pas
