I'm using a "stack" in a separate function (the reason I quote stack is that for my program, it's just an array that I will treat like a stack)... How can I keep track of where I am in my "stack" ?
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I'm using a "stack" in a separate function (the reason I quote stack is that for my program, it's just an array that I will treat like a stack)... How can I keep track of where I am in my "stack" ?
Stack 'pointer'.
That is what a microprocessor uses and they seem to manage OK :)
Push = put value at pointer and increment
pop = take value at pointer minus one and decrement
or vice versa depending on which direction your stack goes.
Code:// untested :)
int stack[100];
int sp=0; //stack pointer
push(x){
stack[sp]=x;
sp++;
}
pop(x){
x=stack[sp-1];
sp--;
}
What am I decrementing exactly? and how?Quote:
Originally Posted by esbo
Pop can only return one value, which is the value on the top of the stack that I want to work with... How can it decrement something?
It decrements the stack pointer.Quote:
Originally Posted by Sparrowhawk
I have updated my earlier post.
Looks quite nice, I may use it my self :)
hmm I need to do this without using a global variable
It's not a global variable; it belongs to your stack object, and is defined in your struct. (That is to say, your stack is more than just an array, right? Right?) If somehow you do just have an array, then every function will just take an extra argument that is your current stack index.Quote:
Originally Posted by Sparrowhawk
Sparrowhawk,
I just finished up my first Comp Sci class where we covered different implementations of stacks using arrays as well as data structures. It's not really practical IMHO to do it with just an array, but see for yourself... Check out Lecture #22, "Stacks and Queues."
http://www.cs.umbc.edu/courses/under...ll08/lectures/
-Dave
Yes it is just an array, no extra functions... Is having 2 args the only way? I seem to remember my prof saying pop took (1 arg, or none ?) while push took (1 or 2).Quote:
Originally Posted by tabstop
Note the stack pointer always points to an empty place.
If it was a stack of trays it would point to one above the stack of trays.
Well it does in my example anyway, you could have it poiint to the top
tray but then usually you start with no trays.
That's great because that's just what lecture #22 addresses. Check it out I'd like to know what you think..Quote:
Originally Posted by Sparrowhawk
-Dave
Quote:
Originally Posted by Sparrowhawk
Why?
Because the variable belongs to the stack, not to the universe?Quote:
Originally Posted by esbo
Edit: I seem to recall (in the spring time, I believe, but I'm not quite bored enough to do a search) someone here who had implemented a stack with a global variable just as you describe. Except he had two stacks. Everything seemed to work fine, until he actually tried to use that second stack....
Ha, I actually found what I needed in there... It was a very simple solution to fix my pop too... Just make a temp value and copy the current value of top to it, use that to return then decrement top itself.Quote:
Originally Posted by mutandis
That seems very obvious all of the sudden. Thanks.
[edit] - The problem I was having was trying to figure out how to return the value while also changing the position without having to take two args.
You could have a single function with a static variable and a direction indicator.
Of course the function is going to be global so your someone can screw your stack up anyway.Code:
//untested
Stackit (x, direction)
{
static int stack[100];
static int sp=0; // can you initialie statics like this???
if (direction==PUSH){
stack[sp]=x;
sp++;
}
else {//POP
x=stack[sp-1];
sp--;
}
}
I would probably use the first method myself, it seems less messy.
i Thought push is assembly ?
It is, that's why I need to create a push & pop function by hand :) since I'm working in CQuote:
Originally Posted by lolguy
It is called push in most assembly languages, but you are using C.Quote:
Originally Posted by lolguy
I don't think C has a 'push' as far as I am aware.
when you using asm with c you do __asm{
or can you use push directly with it ?
The odds that we actually want to push on the system stack is very very very very very small. We want our own stack.Quote:
Originally Posted by lolguy
Z80 assembler stack operations.
Unfortunately it is abit more complicated as the registers are paired
so you push two 8 bit ints to store two paired 8 bit registers.
Also it is 'upside down' the 'top' of the stack is high and as you push stuff
onto it it is stored at lower memory locations.
Code:
PUSH B PUSH BC C5 (SP-2) <- C; (SP-1) <- B; SP <- SP - 2
PUSH D PUSH DE D5 (SP-2) <- E; (SP-1) <- D; SP <- SP - 2
PUSH H PUSH HL E5 (SP-2) <- L; (SP-1) <- H; SP <- SP - 2
PUSH PSW PUSH AF F5 (SP-2) <- Flags; (SP-1) <- A; SP <- SP - 2
--- PUSH IX DDE5 (SP-2) <- IXl; (SP-1) <- IXh; SP <- SP - 2
--- PUSH IY FDE5 (SP-2) <- IYl; (SP-1) <- IYh; SP <- SP - 2
POP B POP BC C1 B <- (SP+1); C <- (SP); SP <- SP + 2
POP D POP DE D1 D <- (SP+1); E <- (SP); SP <- SP + 2
POP H POP HL E1 H <- (SP+1); L <- (SP); SP <- SP + 2
POP PSW POP AF F1 A <- (SP+1); Flags <- (SP); SP <- SP + 2
It is, but it's been part of C since Turbo C/C++ 1.01, that I know of.
It is, except that here we are using terms that are similar thing only implementing them with C.Quote:
Originally Posted by lolguy
Quote:
Originally Posted by lolguy
Yes you can call it what ever you like, call it shove(x) if you like and then pull(x), it's just
an arbitary name of a function.