(* Of course, you could use a FOR loop or a WHILE loop
to solve this problem. *)
end. (* Main *)
Solution to Powers of Two Problem
(* Author: Tao Yue
Date: 13 July 2000
Description:
Display all powers of two up to 20000, five per line
Version:
1.0 - original version
*)
program PowersofTwo;
const
numperline = 5;
maxnum = 20000;
base = 2;
var
number : longint;
linecount : integer;
begin (* Main *)
writeln ('Powers of ', base, ', 1 <= x <= ', maxnum, ':');
(* Set up for loop *)
number := 1;
linecount := 0;
(* Loop *)
while number <= maxnum do
begin
linecount := linecount + 1;
(* Print a comma and space unless this is the first
number on the line *)
if linecount > 1 then
write (', ');
(* Display the number *)
write (number);
(* Print a comma and go to the next line if this is
the last number on the line UNLESS it is the
last number of the series *)
if (linecount = numperline) and not (number * 2 > maxnum) then
begin
writeln (',');
linecount := 0
end;
(* Increment number *)
number := number * base;
end; (* while *)
writeln;
(* This program can also be written using a
REPEAT..UNTIL loop. *)
end. (* Main *)
Note that I used three constants: the base, the number of
powers to display on each line, and the maximum number.
This ensures that the program can be easily adaptable in
the future.
Using constants rather than literals is a good programming
habit to form. When you write really long programs, you
may refer to certain numbers thousands of times. If you
hardcoded them into your code, you'd have to search them
out. Also, you might use the same value in a different
context, so you can't simply do a global Search-and-Replace.
Using a constant makes it simpler to expand the program.
Also note that I used the longint type for the
number variable. This is because to fail the test number <=
20000, number would have to reach 32768, the next power of
two after 16384. This exceeds the range of the integer type: -32768
to 32767. (try it without longint and see what happens)