Implement an array of stacks in C

Question

Implement an array of stacks where stacks are defined :

typedef struct StackNode {

   int data;

   StackNode* next;

} StackNode;

Each array element points to a stack, each stack is initialized as an empty stack. When you start adding elements it will start adding them to the stack in Stacks[0]; if you say -2 in stdin and then 4 for example, the next entries will go to Stacks[4];

For example:

5 10 -2 3 9 7 89 -1
will result in :
Stacks[0] -> 10 -> 5
Stacks[1]
Stacks[2]
Stacks[3] -> 89 -> 7 -> 9

-1 will stop the code from running.

I am having problem with implementing an array of stacks so any help would be appreciated :)

It is not homework, but it is part of the code i am writing and i am trying to finish it as soon as possible. I think I understand everything but the idea of implementing the array. So if this way just a stack to push and pop elements it would've been easy. Thanks for the reply :) — c2009l123
– c2009l123, Commented Nov 12, 2009 at 9:15
Can you post the code that is actually operating on the structure? Or are you having problems even getting started? I think this probably needs the homework tag, as jinguy suggested. — user50049
– user50049, Commented Nov 12, 2009 at 9:16
@c2009l123: Sorry, I had posted that comment as you were writing your reply indicating that to Rom, so I didn't see it until after my comment was posted. — user50049
– user50049, Commented Nov 12, 2009 at 9:37

Amarghosh · Accepted Answer · 2009-11-12 09:27:04Z

2

int t = 0, index = 0;
while(t != -1)
{
  scanf("%d", &t);
  if(t == -2)
  {
    scanf("%d", &t);
    index = t;
    continue;
  }
  if(t >= 0)
    push(stacks[index], t);
}

answered Nov 12, 2009 at 9:27

Amarghosh

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2 Comments

c2009l123 Over a year ago

and push function would just be like push(StackNode *tp, int t) right? i mean not StackNode *tp[int i] or something like that?

Amarghosh Over a year ago

If stacks is an array of pointers to StackNode objects, yeah, your signature for push function is correct.

pmg · Accepted Answer · 2009-11-12 09:16:01Z

2

In line 3 of

typedef struct StackNode {
   int data;
   StackNode* next;          /* line 3 */
} StackNode;

the type StackNode does not yet exist. The type StackNode only begins to exist once the type struct StackNode is fully parsed.

But the type struct StackNode already exists at that point. It is still incomplete, but you can declare pointers to it.

typedef struct StackNode {
   int data;
   struct StackNode* next;          /* line 3 */
} StackNode;

answered Nov 12, 2009 at 9:16

pmg

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1 Comment

c2009l123 Over a year ago

This is not what i am facing a problem with though. For example you can : StackNode *Stacks[10]; to create an array of stacks of size 10. However i am having problem to do operations like pushing for example to a specific number in the array.

Jason Plank · Accepted Answer · 2011-11-21 19:37:25Z

1

You may try something like the following (tested):

//includes
#define SIZE 10


typedef struct StackNode{
 int data ;
 struct StackNode* next ;
}StackNode ;



StackNode* new_stackNode(int num)
{
 StackNode* ptr = (StackNode*)malloc(sizeof(StackNode)) ;
 ptr->data = num ;
 ptr->next = 0 ;
 return ptr ;
}



int main()
{
 StackNode *arr[SIZE] = {0};
 int st_index = 0 ;
 int num = 0 ;
 while(num != -1)
 {
  scanf("%d",&num);
  if( num == -2 )
  st_index++ ;
  else
  {
   StackNode* ptr = new_stackNode(num) ;
   ptr->next = arr[st_index] ;
   arr[st_index] = ptr ;
  }
 }
}

edited Nov 21, 2011 at 19:37

Jason Plank

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answered Nov 12, 2009 at 9:24

sud03r

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Comments

user50049 · Accepted Answer · 2009-11-12 09:22:54Z

0

If you go to the bottom of this Wikipedia article, you'll see an example of what I think you are trying to implement. What you have is a linked list. Additionally, here are some handy doubly linked list helpers which might serve as example.

If you post the actual usage of your code as-is, you might receive a better (more specific) answer.

answered Nov 12, 2009 at 9:22

user50049

Comments

Aaron Digulla · Accepted Answer · 2009-11-12 09:23:29Z

0

You must first get an array of StackNodes:

StackNode ** stacks = malloc(sizeof(StackNode*) * 5); /* allocate 5 stack nodes */
stacks[0] = malloc(sizeof(StackNode)); /* allocate first stack */
...

Now you have a function push(StackNode *, int value). To push on a certain stack, call it with push(stacks[2], value) (to push on the third stack, for example).

answered Nov 12, 2009 at 9:23

Aaron Digulla

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1 Comment

c2009l123 Over a year ago

do i need to do that one by one? what if i have 100 stacks, would i just loop over them? That seems kind of inefficient

unwind · Accepted Answer · 2009-11-12 09:51:05Z

0

This doesn't look like a stack, it looks like a linked list. Of course you can implement stack-like semantics using a linked list, but it's generally not what is meant by "a stack".

To push a new number, you would need to:

Allocate a new StackNode.
Initialize it with the new number.
Link it to the previous.

You could encapsulate this into a function:

void stack_push(StackNode *root, int value)
{
    /* Code omitted */
}

Then you'd just need to provide the proper stack in order to control onto which of your many stacks to push the new number:

stack_push(&Stacks[2], 4711);

edited Nov 12, 2009 at 9:51

answered Nov 12, 2009 at 9:17

unwind

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1 Comment

c2009l123 Over a year ago

I have done that, but how to push the number to a specific stack that is linked to a specific number in the array. For example i want to push number (3) to Stacks[5] or pop a number from Stacks[2]

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