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-08.p
{ Introduction to the Pascal Programming Language
  Dr. Thomas W. MacFarland
  intro_pencil-08.p       
}

{ The purpose of this program is to:

  1.  Demonstrate the selection process used with the if/then  
      conditional branching process.

  2.  Demonstrate the selection process used with the if/then/else 
      conditional branching process.

  3.  Demonstrate how there can be two or more selections within
      a broad conditional statement.

  4.  Demonstrate the begin/end; statements in a conditional block
      statement.

  5.  Demonstrate how the ; character is not used at the end of
      a writeln statement in a multiple if/then/else statement.

  6.  Demonstrate the use of indentation to improve program
      readability.
}

program Demonstrate_If_Then_Else;

var A, B, C : integer;

begin

   A := 5;    
   B := 6;    
   C := 7;    

   writeln('A = ', A:25);
   writeln('B = ', B:25);

   if C = (A + 2) then
     writeln('C = (A + 02) = (05 + 02) = 07');

     if C = (12 - A) then    
       begin
         writeln('C = (12 - A) = (12 - 05) = 07');
       end;

       if B = C then                  
         writeln('B = C')
           else
             writeln('B <> C');

   if B < 3 then                  
     if A < B then
        writeln('B < 3 AND A < B')
          else
            writeln('B may be > 3 OR A may be > B')
              else
                if C = 7 then 
                  writeln('At least it looks like C = 07')
                    else
                      writeln('I need to go back to square one');

end.  { intro_pencil-08.p      } 
% pc PASCAL/intro_pencil-08.p
% a.out
A =                         5
B =                         6
C = (A + 02) = (05 + 02) = 07
C = (12 - A) = (12 - 05) = 07
B <> C
At least it looks like C = 07

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