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-14.p
{ Introduction to the Pascal Programming Language
Dr. Thomas W. MacFarland
intro_pencil-14.p
}
{ The purpose of this program is to:
1. Demonstrate the structure of a while/do loop.
2. Demonstrate a counter variable that increments in
value with each iteration.
3. Demonstrate a counter variable that decrements in
value with each iteration.
}
program Demonstrate_a_While_Do_Loop;
var A, B : integer;
begin
A := 3; {What is the value of A as it }
while A < 8 do begin {ends the 5th loop? What }
write(' A = ', A :4); {happens, because of this }
A := A + 1; {value? }
end; writeln;
writeln(' A = ', A :4); writeln; {What is the value of A now? }
B := 7; {What is the value of B as it }
while B > 2 do begin {enters the loop for the 3rd }
write(' B = ', B :4); {time? What happens, because }
B := B - 3; {of this value? }
end; writeln;
writeln(' B = ', B :4); writeln; {What is the value of B now? }
end. { intro_pencil-14.p }
% pc PASCAL/intro_pencil-14.p
% a.out
A = 3 A = 4 A = 5 A = 6 A = 7
A = 8
B = 7 B = 4
B = 1