Gameboy Development Forum

bkumanchik · 2021-09-07 18:22:57

I'm trying to generate a random number in GBDK between 24 and 144 and I can't seem to get it to work.

My code looks like this: invader_x = rand() % (144 - 24 + 1) + 24; // move invader to random x position

and I have: #include <rand.h> at the top of my code

Any help woulfd be appreciated, thanks

Brian

toxa · 2021-09-08 04:43:41

And what is the problem? It does not compile or produce wrong values? Do you use GBDK-2020?

bkumanchik · 2021-09-08 12:56:44

Wrong values, my sprite ends up off the left side of the screen sometimes.

bkumanchik · 2021-09-15 18:15:11

Anybody?

toxa · 2021-09-15 18:57:37

Do you use GBDK-2020?

bkumanchik · 2021-09-16 13:47:17

Yes, and I'm including rand.h

toxa · 2021-09-16 15:09:48

you must offset your sprite 8 pixels by X. top-left corner of visible screen for sprites is: X==8, Y==16

bkumanchik · 2021-09-16 15:50:23

Is this the correct code to generate a random number between 24 and 140?

invader_x = rand() % (140 - 24 + 1) + 24;

Also is this all I need above in my code to set it up?

void initarand (uint8_t seed );

I'm still having trouble getting this to work

toxa · 2021-09-17 11:17:36

bkumanchik wrote:
invader_x = rand() % (140 - 24 + 1) + 24;

rand() returns a signed char which is -128..127. to make rand() return a positive value within 0..255 you must cast it to unsigned char:

Code:

r = ((unsigned char)rand() % (140 - 24 + 1)) + 24;

bkumanchik · 2021-09-17 11:29:38

Thanks, I'll try that

bkumanchik · 2021-09-17 19:08:51

That did it, Thanks!

Gameboy Development Forum

#1 2021-09-07 18:22:57

I'm trying to generate a random number in GBDK

#2 2021-09-08 04:43:41

Re: I'm trying to generate a random number in GBDK

#3 2021-09-08 12:56:44

Re: I'm trying to generate a random number in GBDK

#4 2021-09-15 18:15:11

Re: I'm trying to generate a random number in GBDK

#5 2021-09-15 18:57:37

Re: I'm trying to generate a random number in GBDK

#6 2021-09-16 13:47:17

Re: I'm trying to generate a random number in GBDK

#7 2021-09-16 15:09:48

Re: I'm trying to generate a random number in GBDK

#8 2021-09-16 15:50:23

Re: I'm trying to generate a random number in GBDK

#9 2021-09-17 11:17:36

Re: I'm trying to generate a random number in GBDK

bkumanchik wrote:

Code:

#10 2021-09-17 11:29:38

Re: I'm trying to generate a random number in GBDK

#11 2021-09-17 19:08:51

Re: I'm trying to generate a random number in GBDK

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