Introduction to the Pascal Programming Language

© 1998 by Dr. Thomas W. MacFarland -- All Rights Reserved

     Instructions:   Review the following program and see if you can 
                     predict the outcome by completing a "pencil 
                     trace" of the code.  

                     Program output is provided at the end of this 
                     page.

     Compiler:       The program was prepared using Standard Pascal 
                     on a UNIX-based host computer.

% cat PASCAL/intro_pencil-10.p
{ Introduction to the Pascal Programming Language
  Dr. Thomas W. MacFarland
  intro_pencil-10.p       
}

{ The purpose of this program is to:

  1.  Demonstrate the Boolean operators:  and, or, not.

  2.  Demonstrate the use of a negative number in a counter-
      type loop.
}

program Demonstrate_Boolean_Operators_in_a_Loop;

var X : integer;

begin

   for X := -10 to -5 do begin
     if (X <> -7) and (X <> -6) then
        write('  X = ',X:3);
   end; writeln; writeln;

   for X := -10 to -5 do begin
     if (X <> -7) or (X <> -6) then
       write('  X = ',X:3);
   end; writeln; writeln;

   for X := -10 to -5 do begin
     if not (X <> -7) and (X <> -6) then
       write('  X = ',X:3);
   end; writeln; writeln;

end.  { intro_pencil-10.p      } 
% pc PASCAL/intro_pencil-10.p
% a.out
  X = -10  X =  -9  X =  -8  X =  -5

  X = -10  X =  -9  X =  -8  X =  -7  X =  -6  X =  -5

  X =  -7

Please send comments or suggestions to Dr. Thomas W. MacFarland