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MDP3.PAS
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Pascal/Delphi Source File
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1992-03-01
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2KB
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56 lines
program mdp3;
{Program to accompany article in issue #10 of the Pascal NewsLetter. }
{Author: Mitch Davis, (3:634/384.6) +61-3-890-2062. }
{This program is a demonstration on how you can make a scroller. Use the }
{+/- keys, and q to quit. This algorithm is used later. }
uses crt;
const ScreenLen = 24;
LineCount = 100;
WinTop:integer = 1; {Note MUST be integer}
var loop:byte;
ch:char;
function Min (a,b:word):word;
{Returns the smaller of the two parameters}
begin
if a < b then Min := a else Min := b;
end;
begin
{Draw the initial screen}
gotoxy (1,1);
for loop := 1 to min (ScreenLen,LineCount-WinTop+1) do writeln (loop,' ');
write ('*** Use ''+'' to move forward, ''-'' to move back. ''q'' to quit.');
{do the scrolling}
repeat
ch := readkey;
case ch of
'-':if WinTop > 1 then begin
dec (WinTop);
gotoxy (1,ScreenLen); {bottom of the screen}
DelLine;
gotoxy (1,1); {top of the screen}
InsLine;
write (WinTop); {the new line}
end;
'+':if WinTop < LineCount-ScreenLen+1 then begin
inc (WinTop);
gotoxy (1,1); {top of the screen}
DelLine;
gotoxy (1,ScreenLen); {bottom of the screen}
InsLine;
write (WinTop+ScreenLen-1); {the new line}
end;
'q':; {ensure that it doesn't beep if q is pressed.}
else write (#7); {beep}
end;
until ch = 'q';
end.