For loops with type byte (*solved*)

[boriel]

Code:

dim c,b as byte


FOR c=1 TO 175
FOR b=1 TO 250
  PLOT b,c
NEXT b
NEXT c

Doesn't seem to work as expected. If I make it a uinteger, it works perfectly.

You must use ubyte (Unsigned Byte), since byte type is signed, and in the above lines, you have an overflow:
ubyte 175 is -85 byte => the FOR loop is skipped. In the future, the compiler might issue an overflow warning in these cases to warn you about this.

1> Would for/next loops with byte be faster? (I'm following the principle of smaller=faster)

It should be. Z80 is an 8 bit machine and the FOR is done with 8bit values when using bytes.
If you can understand Z80 ASM (I guess you do ) compile your program with --asm and have a look at the output.