Hello there,

I Need some help with some old basic code.
I am translating a game (written in msx basic ) in Visual Basic.

Most of the code can be used as written
But there are some pieces in the code that i can't figure out.

Those pieces are:

1) if x or y then return
2) if not S then
3) p=gv+d1+10*(gv=30 and c=0) + (gv=3 and p=0)
4) SW=P=5


I have many years experience in programming but never saw code like this before.

Any one who can help me??


Thanx

>I have many years experience in programming

Really ?

"=", "or", "not" are boolean operations

Try to execute statements like

PRINT 5=5
PRINT not 6=7

and you will know what to expect.

Quote:

Hello there, I Need some help with some old basic code. I am translating a game (written in msx basic ) in Visual Basic. Most of the code can be used as written But there are some pieces in the code that i can't figure out. Those pieces are: 1) if x or y then return 2) if not S then 3) p=gv+d1+10*(gv=30 and c=0) + (gv=3 and p=0) 4) SW=P=5 I have many years experience in programming but never saw code like this before.

Then you've never seen (MSX) BASIC before

Any boolean expression--like (X OR Y) or (P=5)--returns either 0, when false, or -1, when true. Not only in BASIC, but also in a lot of other 3rd gen programming languages! So, if P really equals 5, the expression (P=5) equals -1, else it is 0.

maybe you'd feel more confy with the following equivalents of the above statements:

1) IF X<>0 OR Y<>0 THEN RETURN
2) IF S=0 THEN
3) IF GV=30 AND C=0 THEN
        P=GV+D1+10*-1 + 0 ' If GV=30, GV cannot be 3, so the expression (GV=3 AND P=0) is false and therefore 0
        ELSE
            IF GV=3 AND P=0 THEN
                 P=GV+D1+10 * 0 + -1 'see comment above
            ELSE
                 P=GV+D1+10 * 0 + 0
4) IF P=5 THEN SW=-1 ELSE SW=0

But that's real n00b and you won't find code like that in a program written by someone with years of programming experience

Boolean expressions in basic result in -1 (true) or 0 (false).

1) plain boolean logic, but consider x and y as booleans, like this: if (x==-1 || y==-1)
2) see 1)
3) use the -1 and 0
4) this is just chain-assignment. sw=5=5 This is also valid in C, e.g.


EDIT: darn, Auroor was just before me. You'll see constructions like this a lot in one-liners, because it's the only way to avoid if...then

Quote:

4) this is just chain-assignment. sw=5=5 This is also valid in C, e.g.

Buzz!

Edit: Oh, and Buzz! on your 1), too

Quote:

"=", "or", "not" are boolean operations

Actually "or", "not" and "and" are bitwise operators in MSX basic. (1 and 2) yields 0 not true.
The "=" can have two roles
- assignment as in 'a=38' or 'SW=P=5'
- comparison as in 'if a=42 then ...' of 'SW=P=5'
the first role is only used when the "+" is only preceded by a variable (or the keyword "let" plus a variable name).

The value of (x=y) is -1 if x and y are equal and 0 otherwise.
In memory -1 is represented with all bits equal to one, so this choice ensures that (not (x=y)) has the same value as (x<>y).
Msx basic does not have an Iif function or ?: operator, but with some arithmetic operations you can often avoid using 'if..then..' when what you want to have can achieved with the ?: operator. It's not good for readability though.

Edited: bold ='s, added: hmm, two people beat me to posting a reaction, fixed typo.

Quote:

Hello there, I Need some help with some old basic code. I am translating a game (written in msx basic ) in Visual Basic. Most of the code can be used as written But there are some pieces in the code that i can't figure out. Those pieces are: 1) if x or y then return 2) if not S then 3) p=gv+d1+10*(gv=30 and c=0) + (gv=3 and p=0) 4) SW=P=5 I have many years experience in programming but never saw code like this before. Any one who can help me?? Thanx

all those sentences are directly executable in VB5 or 6 (also QBASIC)

I think you scared the new kid away

Quote:

2) IF S=0 THEN

BUZZ!
2) IF S <> -1 THEN

Remember "NOT" is a bitwise operator in MSX Basic