# Difference between revisions of "Solution 3"

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3Ea - Solutions (author: Tao Yue, state: unchanged) | 3Ea - Solutions (author: Tao Yue, state: unchanged) | ||

## Revision as of 11:30, 13 December 2013

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3Ea - Solutions (author: Tao Yue, state: unchanged)

**Solution to Fibonacci Sequence Problem**

```
(* Author: Tao Yue
Date: 19 July 1997
Description:
Find the first 10 Fibonacci numbers
Version:
1.0 - original version
*)
program Fibonacci;
var
Fibonacci1, Fibonacci2 : integer;
temp : integer;
count : integer;
begin (* Main *)
writeln ('First ten Fibonacci numbers are:');
count := 0;
Fibonacci1 := 0;
Fibonacci2 := 1;
repeat
write (Fibonacci2:7);
temp := Fibonacci2;
Fibonacci2 := Fibonacci1 + Fibonacci2;
Fibonacci1 := Temp;
count := count + 1
until count = 10;
writeln;
(* 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)

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