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` a simple exercise for DBPro coders with nothing better to do :)

` Step 1: Run this code and note what happens.
` Step 2: Comment out all the cls's and run the code again.
` Step 3: Explain why you see what you see.

` Cooding is fun!

sync on: sync

dim c$(23)

for i = 1 to 5
  print "<"+c$(i)+">"
next i

print "... press <return> to continue"

sync

while returnkey() = 0
endwhile

`cls

for i = 1 to 5
  c$(i) = ""
next i

print "((<<"+c$+">>))"

print "... press <control> to continue"

sync

while controlkey() = 0
endwhile

`cls

for i = 0 to 5
  c$(i)= "ABCDE"
next i

print "<<"+c$+">>"

print "... press <spacekey> to continue"

sync

while spacekey() = 0
endwhile

`cls

c$ = "ABCDEFG"
print c$
for i = 0 to 5
  print "["+c$(i)+"]"
next i
print "... press <shiftkey> to continue"
sync

while shiftkey() = 0
endwhile

end

// skipping the sync and keypress commands

make an array
print out the secons to the sixth element, which is an empty string

set the second to the sixth element to an empty string
print out c$ which is an empty string. ( c =/= c$ =/= c$() )

set the first to the sixth element to ABCDE
print out c$, which is still an empty string

set c$ to ABCDEFG
print out c$
print out the first to the sixth element, which are all set to ABCDE.

// expected output:
""
""
""
""
""

""

""

"ABCDEFG"
"ABCDE"
"ABCDE"
"ABCDE"
"ABCDE"
"ABCDE"
"ABCDE"

// actual output:
<>
<>
<>
<>
<>
... press <return> to continue
((<<>>))
... press <control> to continue
<<>>
... press <spacekey> to continue
ABCDEFG
[ABCDE]
[ABCDE]
[ABCDE]
[ABCDE]
[ABCDE]
[ABCDE]

// this code will count from 0 to someHighNumber, as fast as it can, using a for loop
// the loop does not call sync, therefore it will not update the screen. it will look like the programm crashed, do not worry. (this is actually a major hint to the solution)
// the last thing it outputs is how long it took to finish in seconds.

// step 0: change "someHighNumber" to something so the loop takes about 10 seconds so you do not have to wait so long for a result
someHighNumber=60*2000     // <-------

// step 1: run the programm and note how long it took to finish
// step 2: take a stopwatch, run the programm again and press ESC to immediately exit the programm while the loop runs.
//              check how long it took to exit the programm. try to explain the result.
// step 3: comment out the for loop and activate the while loop.
//              try to explain the difference.
// step 4: activate this line:
// text 0,0,"Hallo Welt"
//              and run the programm again. try to move the window around. try to explain what you see.

time=timer()
sync on
sync

for i=0 to someHighNumber
    print i  
NEXT i

remstart
i=0
while i<=someHighNumber
    print i
    inc i
ENDWHILE
remend

print (timer()-time)/1000
sync
wait key
end

every loop makes some kind of callback to the OS at the end of the loop (do *loop* / while *endwhile* / repeat *until*), with the exception of a for loop.
without that callback, the OS assumes that the programm has crashed because it does not "respond".
my guess is that ESC tells the OS to shut down the programm at the next callback, which is after the whole for loop.

that makes the for loop much faster than any other loop, because it skips callback.

if you make a simple:
    print "Hello World"
    wait key
programm,
you will be able to run it on any windows os from windows 95 and up.
i guess this is because the dbpcompiler (maybe?) only links directx9 if you actually use non basic commands.
since directx9 is not linked, the sync commands do not work as intended.
the text command changes this. directx9 will be linked and the sync command will work properly.

if you move around the window, a callback will be made and the screen will be updated even without a sync command. which is a total guess.

` this program attempts to test the theory that a for/next loop is potentially much faster than
` an equivalent loop using do/loop, while/endwhile or repeat/until because of the absence of callbacks

` it's possible that the DBPro overhead of adding the extra exit test in the for/next loop will
` outweigh this advantage (it doesn't seem to on my machine)

` on my machine and using DBPro9Ex, the for/next loop is somewhat, but consistently, faster than the other three
` which are very similar to each other

` typical results for me are:
`   for/next       : 3638 loops per ms
`   do/loop        : 3356
`   while/endwhile : 3367
`   repeat/until   : 3375

sync on
sync

text 20, 20, "press numeric key to exit for/next loop"

sync

sum = 0
timeNow = timer()

for i  = 0 to 1 step 0
  inc sum
  if scancode() <> 0 then exit
next i

timeTaken = timer()-timeNow
speed1 = sum/timeTaken ` integer division should be fine here

cls
text 20, 40, "press numeric key to exit do/loop"
sync

while scancode() <> 0 ` need to wait for previous scancode to clear
endwhile

sum = 0
timeNow = timer()
do
  inc sum
  if scancode() <> 0 then exit
loop

timeTaken = timer()-timeNow

speed2 = sum/timeTaken ` integer division should be fine here

cls
text 20, 60, "press numeric key to exit while/endwhile"
sync

while scancode() <> 0 ` need to wait for previous scancode to clear
endwhile
sum = 0
timeNow = timer()

while scancode() = 0
  inc sum
endwhile

timeTaken = timer()-timeNow
speed3 = sum/timeTaken ` integer division should be fine here

cls
text 20, 80, "press numeric key to exit repeat/until"
sync

while scancode() <> 0 ` need to wait for previous scancode to clear
endwhile
sum = 0
timeNow = timer()

repeat
  inc sum
until scancode() <> 0

timeTaken = timer()-timeNow
speed4 = sum/timeTaken ` integer division should be fine here

cls
print "(for/next):  loops per ms = ", speed1

print "(do/loop)  loops per ms = ", speed2

print "(while/endwhile)  loops per ms = ", speed3

print "(repeat/endwhile)  loops per ms = ", speed4

sync
wait key

end

Log Name:      Application
Source:        Application Error
Date:          17/07/2017 21:36:54
Event ID:      1000
Task Category: (100)
Level:         Error
Keywords:      Classic
User:          N/A
Computer:      DESKTOP-6I7I0DT
Description:
Faulting application name: landscapeShowcase.exe, version: 1.0.0.0, time stamp: 0x4d460aea
Faulting module name: unknown, version: 0.0.0.0, time stamp: 0x00000000
[quote=]Exception code: 0xc0000005
Fault offset: 0x00000000
[/quote]Faulting process ID: 0x2b38
Faulting application start time: 0x01d2ff3c6ceb6f68
Faulting application path: C:\Users\jimbu\Documents\My Games Software\Dark Basic Professional\Talks\Launceston Computer Club\LandscapeShowcase\landscapeShowcase.exe
Faulting module path: unknown
Report ID: 8ceb4e73-fea9-40f9-9c03-c4358aa455f3
Faulting package full name: 
Faulting package-relative application ID: 
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Application Error" />
    <EventID Qualifiers="0">1000</EventID>
    <Level>2</Level>
    <Task>100</Task>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2017-07-17T20:36:54.510612600Z" />
    <EventRecordID>2860</EventRecordID>
    <Channel>Application</Channel>
    <Computer>DESKTOP-6I7I0DT</Computer>
    <Security />
  </System>
  <EventData>
    <Data>landscapeShowcase.exe</Data>
    <Data>1.0.0.0</Data>
    <Data>4d460aea</Data>
    <Data>unknown</Data>
    <Data>0.0.0.0</Data>
    <Data>00000000</Data>
    <Data>c0000005</Data>
    <Data>00000000</Data>
    <Data>2b38</Data>
    <Data>01d2ff3c6ceb6f68</Data>
    <Data>C:\Users\jimbu\Documents\My Games Software\Dark Basic Professional\Talks\Launceston Computer Club\LandscapeShowcase\landscapeShowcase.exe</Data>
    <Data>unknown</Data>
    <Data>8ceb4e73-fea9-40f9-9c03-c4358aa455f3</Data>
    <Data>
    </Data>
    <Data>
    </Data>
  </EventData>
</Event>

set display mode desktop width(), desktop height(), 32
sync on : sync rate 60: sync

autocam off
position camera 0, 200, 0
point camera 0, 0, 0
color backdrop rgb (0,0,0)

make object plane 1, 100, 100, 24, 24
color object 1, rgb(0, 255, 0)

repeat
  sync
until spacekey()

end