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-05.p
{ Introduction to the Pascal Programming Language
  Dr. Thomas W. MacFarland
  intro_pencil-05.p       
}

{ The purpose of this program is to:

  1.  Demonstrate the use of real variables and how these 
      variables can appear when printed using simple format 
      operations.  

  2.  Demonstrate how a variable can easily change value, if 
      appropriately directed in the program.  

  3.  Demonstrate the use of e-notation.
}

program Demonstrate_the_use_of_Reals_and_E_Notation;

var A,B,C,D : real;

begin

   A := 1.234;               
   B := A + 5.678;           
   C := B - A;               
   D := (9.101) * (A/B);           

   write('   A = ',A:6); writeln(' A = ',A:6:3);
   write('   B = ',B:6); writeln(' B = ',B:6:3);
   write('   C = ',C:6); writeln(' C = ',C:6:3);
   write('   D = ',D:6); writeln(' D = ',D:6:3); writeln;

   D := (4.5) / (B * 6.78);               

   write('   A = ',A:6); writeln(' A = ',A:6:3);
   write('   B = ',B:6); writeln(' B = ',B:6:3);
   write('   C = ',C:6); writeln(' C = ',C:6:3);
   write('   D = ',D:6); writeln(' D = ',D:6:3); writeln;

   D := B - (A/B);               

   write('   A = ',A:6); writeln(' A = ',A:6:3);
   write('   B = ',B:6); writeln(' B = ',B:6:3);
   write('   C = ',C:6); writeln(' C = ',C:6:3);
   write('   D = ',D:6); writeln(' D = ',D:6:3); writeln;

end.  { intro_pencil-05.p      } 
% pc PASCAL/intro_pencil-05.p
% a.out
   A = 1.2e+00 A =  1.234
   B = 6.9e+00 B =  6.912
   C = 5.7e+00 C =  5.678
   D = 1.6e+00 D =  1.625

   A = 1.2e+00 A =  1.234
   B = 6.9e+00 B =  6.912
   C = 5.7e+00 C =  5.678
   D = 9.6e-02 D =  0.096

   A = 1.2e+00 A =  1.234
   B = 6.9e+00 B =  6.912
   C = 5.7e+00 C =  5.678
   D = 6.7e+00 D =  6.733


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