Array length: Difference between revisions

=={{header|Z80 Assembly}}==

Arrays don't have an "end" as defined by the language, so there are a couple ways to mark the end of an array. One is with a null terminator, and the other is with a pre-defined size byte stored at the beginning. Using a null terminator isn't the best choice for a general-purpose array since it means your array cannot contain that value anywhere except at the end. However, since having the size already determined defeats the purpose of this task, the null-terminator method will be used for this example.

The simplest way to implement an array of variable-length strings is to have the array contain pointers to said strings rather than the strings themselves. That way, the elements of the array are of equal length, which makes any array <b>much</b> easier to work with.

<lang z80> org &8000

ld hl,TestArray

call GetArrayLength_WordData_NullTerminated

call Monitor ;show registers to screen, code omitted to keep this example short

ReturnToBasic:

RET

GetArrayLength_WordData_NullTerminated:

push hl ;we'll need this later

loop_GetArrayLength_WordData_NullTerminated

ld a,(hl) ;get the low byte

ld e,a ;stash it in E

inc hl ;next byte

ld a,(hl) ;get the high byte

dec hl ;go back to low byte, otherwise our length will be off.

or a ;compare to zero.

jr nz,keepGoing

cp e ;compare to E

jr z,Terminated_GetArrayLength ;both bytes were zero.

KeepGoing:

inc hl

inc hl ;next word

jp loop_GetArrayLength_WordData_NullTerminated ;back to start

Terminated_GetArrayLength:

pop de ;original array address is in DE

or a ;clear the carry

sbc hl,de ;there is no sub hl,de; only sbc

srl h

rr l ;divide HL by 2, since each element is 2 bytes.

ret ;returns length in hl</lang>

{{out}}

<pre> (HL contains length of the array)

HL:0002

</pre>