Variables: Need clarification

Oldbitcollector (Jeff)

I have to admit that I'm getting very lost in variables.
Would someone mind giving me some examples in .spin based on these basic examples?

A$="This is not a number"

A=1

A=A+1

A=A-1

LET B = A

If there is some clarification elsewhere in print, (the prop manual isn't helping)
please point in that direction. Thanks!

Jeff

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The comments and code above are proof that a million monkeys with a million propeller chips *could* write Shakespeare!

Mike Green

1) There are no string variables in Spin, but you can use string constants and byte arrays to do some of the same functions. In this case, you'll need to declare a method to do the string copy using primitives included in Spin. Note that there's not checking for overflow of the variable. You could add checking to strcopy if you need to.

VAR byte a[noparse][[/noparse] 20 ]

PUB strcopy( dst, src)
   bytemove(dst, src, strsize(src)+1)

{ now you can do: strcopy(a,string("This is not a number")) }

2) A := 1

3) A := A + 1 or A += 1 or A++

4) A := A - 1 or A -= 1 or A--

5) B : = A

deSilva

To anticipate a further question:

.......  string("xxxxxxxxxx") ......

is nearly exactly the same as:

......... @s9876543 ........

DAT
s9876543 BYTE "xxxxxxxxxx",0

Edit: STRING is very versatile: You can also write things like :

string("ABC",10,200,"XYZ",13)

Of course you must not use 0...

Post Edited (deSilva) : 7/31/2007 5:18:30 PM GMT

Fred Hawkins

deSilva said...
Of course you must not use 0...

I assume you mean ascii $00, not ascii 48, "0".

Mike Green

Fred,
Strings in Spin use a zero byte ($00) as a terminator character, like in C and some other programming languages.

Oldbitcollector (Jeff)

Forgive me... But why does this work?

VAR byte a[noparse][[/noparse] 20 ]

[noparse][[/noparse]set the length of a?]

PUB strcopy( dst, src) [noparse][[/noparse]a function with destination and source?]
bytemove(dst, src, strsize(src)+1) [noparse][[/noparse]move destination to source +1??]

{ now you can do: strcopy(a,string("This is not a number")) }

so a now equals "This is not a number" ?

Lost...

Oldbitcollector

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The comments and code above are proof that a million monkeys with a million propeller chips *could* write Shakespeare!

Mike Green

bytemove requires a byte count as well as the address of the data and the address of where to put it.

strsize scans the string looking for a zero byte and returns the number of non-zero bytes found before the zero byte which is the length of the string. strsize+1 includes the zero byte in the length.

The declaration "VAR byte a[noparse][[/noparse] 20 ]" simply allocates a 20 byte block of storage.

I did make a mistake in the example in the comment. It should be: strcopy(@a,string("This is not a number"))
The difference is that the "@" operator produces an address (of a) which is what strcopy expects. The "string" function already returns an address.

deSilva

Mike Green said...
The "string" function already returns an address.

STRING should be called a "compiler directive" rather then a "function". Note that it has all the limitations constant expressions have..