Stack Program Here

Code:

---


#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>


struct stack {
    int  sdata;
        struct stack *next;
} ;

struct stack *Push (struct stack *llist, int data);
struct stack Pop (struct stack ** llist);
void ReleaseStack(struct stack * llist);

int main () {
    struct  stack  *llist = NULL;
    int  data, choice;

    do
        {
                printf("\nEnter choice (1: Push) (2: Pop) (3: end) : ");
                scanf("%d",&choice);
                while(getchar() != '\n') continue;

                switch (choice)
                {
                        case 1:
                                printf ("Integer to Push onto the stack: ");
                                scanf ("%d", &data);
                                //clear memory buffer
                                while(getchar() != '\n') continue;
                                llist = Push(llist,data);
                                break;
                        case 2:
                                if (llist == NULL)
                                {
                                        printf ("stack empty!\n");
                                }else
                                {
                                        struct stack temp = Pop(&llist);
                                        printf("%d Popped.\n", temp.sdata);
                                }

                        case 3:
                                break;

                  default:
                                printf ("Invalid menu choice - try again\n");
                                break;
                }

    } while (choice != 3);

    ReleaseStack(llist);

        return 0;
}       



struct stack * Push(struct stack * llist, int data)
{
        struct stack *newp = NULL;

        if(llist == NULL)
        {
                newp = (struct stack  *) malloc (sizeof (struct stack));
                newp->next = NULL;
                newp->sdata = data;
                llist = newp;
                return llist;
        }else
        {
                newp = (struct stack  *) malloc (sizeof (struct stack));
                newp->sdata = data;
                newp->next = llist;
                return newp;
        }

}

struct stack Pop (struct stack ** llist)
{
        //holds the return value (data)
        struct stack temp;
        //use to free the head node
        struct stack *freep = *llist;

        //reposition the head of the stack for post Pop
        if((*llist)->next == NULL)
        {
                *llist = NULL;
                temp = *freep;
                free(freep);
        }else
        {
                *llist = (*llist)->next;
       
                //get data value
                temp = *freep;

                //free head node
                free(freep);
        }

        return temp;

 }

void ReleaseStack(struct stack * llist)
{
        while(llist != NULL)
        {
                printf("releasing %d\n", Pop(&llist));
        }
}

---

Here is a stack program. It seems to be the topic of the day. This is the stack program that I wrote this morning.

Ohh goody - here's my attempt.

Code:

---

#include <stdio.h>
#include <stdlib.h>

struct stack {
    int          data;
    struct stack *next;
};

// push to front
// way simpler than push to rear
void push ( struct stack **head, int val ) {
    struct stack *node = malloc( sizeof(struct stack) );
    node->data = val;
    node->next = *head;
    *head = node;
}
int pop ( struct stack **head ) {
    struct stack *node = *head;
    int result = node->data;
    *head = (*head)->next;
    free( node );
    return result;
}

int main ( ) {
    struct stack *s = NULL;    // its empty
    int i;
    for ( i = 0 ; i < 10 ; i++ ) {
        push( &s, i );
    }
    for ( i = 0 ; i < 10 ; i++ ) {
        printf( "%d\n", pop(&s) );
    }
    printf( "The stack is %sempty\n", s == NULL ? "" : "not " );
    return 0;
}

---

If you push and it is empty than it crashes. I should have also used a pointer to a pointer to update main for my push function. I did that for my pop function. Why didn't I do it for the push? Also you add the node to the head of the stack, ofcourse, this is true for a stack.

> If you push and it is empty than it crashes.

> *head = node;
this updates the variable s in main, not what s points to.

I put this line of code in the push loop, and it al looks good.
printf( "%p %p\n", s, s->next );

Actually your code is very clear. I understand it perfectly. This is similar to my code, for the pop function. I was just saying that if you pop too many times than the program crashes. There is no error checking. I had a hard time this morning making mine bulletproof. I have it now but I could revise the push function so that it is automatically updated. I wasn't used to using pointers to pointers. When you pop the last node in the stack, I didn't know where to put the head pointer until I realized I should set it to NULL. I was also having difficulties freeing the poped node but I finally figured it out.

> I was just saying that if you pop too many times than the program crashes.
Well I was confused when you said push in the previous message.

> There is no error checking.
As they say in books "left as an easy exercise for the reader" . :p

For some reason this was not a simple exercise for me this morning. It took me a few hours to figure it out.

I'll post mine again. It does use pointers, but rather differently to what has been done here. It is using a simple contiguos stack.