I have seen other people's source code but I can't get it to work.
On my tests I do:

.SAVE
getCalc("appvarTest")->M
repeat getkey(15)
output(1,1,M dec,i) //basically output m
if getkey(10)
M+1->M
end
end
M->{getCalc("appvarTest")}



If the appvar is in ram, that is

So i did this:
.SAVE
{getCalc("appvarTest")}->M
repeat getkey(15)
output(1,1,M dec,i) //basically output m
if getkey(10)
M+1->M
end
end
M->{getCalc("appvarTest")}
and it still didn't work... help?

so I did this:.SAVE
!if {getCalc("appvarTest")}->M
->{getCalc("appvarTest")}
end
repeat getkey(15)output(1,1,M dec,i) //basically output m
if getkey(10)
M+1->M
end
end
M->{getCalc("appvarTest")}
And when I check the appvar list, it isn't there. and I also use 2nd 8
Also, I am adding a new class called mage and I am adding skills that you can use.

then you have to create it first.
Just make a seperate prog like this to create it:
getCalc("appvTest",2)

Why would you need a separate program to create it? You can simply create it if it doesn't already exist from your main program logic, like:

"appvTest"→Str0
!If GetCalc(Str0)
  GetCalc(Str0,2)
End
→V

Then, you'd have a reference to the appvar in the variable V. Alternatively, a solution with a bit more robustness, which works if the appvar is archived and handles the case in which allocation failed:

"appvTest"→Str0
UnArchive Str0
!If GetCalc(Str0)
  !If GetCalc(Str0,2)
    .Failed to create appvar, handle error somehow
  End
End
→V

Then you'd probably want to Archive Str0 before your program ends so it doesn't get lost in a random RAM clear.

That's what he did ?

I made the game so that once you click and release the button, you attack instead of holding the button, but if you hold the button for a while, then release you do a power attack which does double damage and is quicker.

Another alternative to appvars would be self-modifying code, but then the game cannot be an app nor a nostub program. Else there's the old school password save system trick, which is hard to make secure.