Stack implimentation using Linkedlist in C - c

Question

I have written a code in C language to implement a stack using LinkedList algorithm. Here is the code........
#include<stdio.h>
#include<stdlib.h>
#include<limits.h>
struct listNode {
int data;
struct listNode *next;
};
struct stack{
struct stack *top;
};
struct stack *createstk(){
struct stack *stk;
stk=malloc(sizeof(struct stack));
stk->top=NULL;
return stk;
}
void push(struct stack *stk,int data){
struct listNode *temp;
temp=malloc(sizeof(struct listNode));
if(!temp){
printf("heap overflow");
return;
}
temp->data=data;
temp->next=stk->top;
stk->top=temp;
}
int pop(struct stack *stk){
if(isEmpty(stk))
return INT_MIN;
int data;
struct listNode *temp;
temp= stk->top;
stk->top=stk->top->next;
data=temp->data;
delete(temp);
return data;
}
int peek(struct stack *stk){
if(isEmpty(stk))
return INT_MIN;
return stk->top->data;
}
int isEmpty(struct stack *stk){
return stk->top==NULL;
}
void deleteStack(struct stack *stk){
struct listNode *temp,*p;
p=stk->top;
while(p){
temp=p->next;
p=p->next;
free(temp);
}
free(stk);
}
int main(){
int i=0;
struct stack *stk=createstk();
for(i=0;i<=10;i++)
push(stk,i);
printf("Top Element is %d",peek(stk));
for(i=0;i<=10;i++){
printf("popped element is %d",pop(stk));
}
if(isEmpty(stk))
printf("stack is empty");
else
printf("stack is not empty");
deleteStack(stk);
return 0;
}
[warning]assignment from incompatible pointer type.
As you can see above in the picture. I am a newbie in coding world and facing this error first time. That's why I don't know what to do. Please tell me...

Answer 1

The field top in the type stack has the wrong type. Change
struct stack {
struct stack *top;
};
to
struct stack {
struct listNode *top;
};

Answer 2

Your have a large number of error beginning with the incorrect type for stack->top, as correctly noted by August Karlstrom your type for the member top must be struct listNode *top;, e.g.
struct stack {
struct listNode *top;
};
Following the correction, you must either reorder your functions or provide function prototypes for isEmpty() and deleteStack(). Moving them up in your code before before their first use will solve the problem, e.g.
struct stack *createstk()
{
struct stack *stk;
stk = malloc (sizeof (struct stack));
stk->top = NULL;
return stk;
}
int isEmpty (struct stack *stk)
{
return stk->top == NULL;
}
void deleteStack (struct stack *stk)
{
struct listNode *temp, *p;
p = stk->top;
while (p) {
temp = p->next;
p = p->next;
free (temp);
}
free (stk);
}
...
Next, this is C, not C++ there is no delete function to free memory, so in pop(), you must call free (temp); instead of delete (temp);.
Finally, provide spacing to make your code readable. Incorporating the above, you could do the following:
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
struct listNode {
int data;
struct listNode *next;
};
struct stack {
struct listNode *top;
};
struct stack *createstk()
{
struct stack *stk;
stk = malloc (sizeof (struct stack));
stk->top = NULL;
return stk;
}
int isEmpty (struct stack *stk)
{
return stk->top == NULL;
}
void deleteStack (struct stack *stk)
{
struct listNode *temp, *p;
p = stk->top;
while (p) {
temp = p->next;
p = p->next;
free (temp);
}
free (stk);
}
void push (struct stack *stk, int data){
struct listNode *temp;
temp = malloc (sizeof *temp);
if (!temp) {
perror ("push()-malloc-temp");
return;
}
temp->data = data;
temp->next = stk->top;
stk->top = temp;
}
int pop(struct stack *stk){
int data;
struct listNode *temp;
if (isEmpty(stk))
return INT_MIN;
temp = stk->top;
data = temp->data;
stk->top = stk->top->next;
free (temp);
return data;
}
int peek(struct stack *stk){
if(isEmpty(stk))
return INT_MIN;
return stk->top->data;
}
int main (void) {
int i=0;
struct stack *stk=createstk();
for (i = 0; i <= 10; i++)
push(stk,i);
printf("Top Element is %d\n",peek(stk));
for (i = 0; i <= 10; i++)
printf (" popped element is %d\n",pop(stk));
if (isEmpty(stk))
printf ("stack is empty\n");
else
printf ("stack is not empty\n");
deleteStack(stk);
return 0;
}
Example Use/Output
$ ./bin/stack_ll
Top Element is 10
popped element is 10
popped element is 9
popped element is 8
popped element is 7
popped element is 6
popped element is 5
popped element is 4
popped element is 3
popped element is 2
popped element is 1
popped element is 0
stack is empty
Memory Use/Error Check
In any code you write that dynamically allocates memory, you have 2 responsibilities regarding any block of memory allocated: (1) always preserve a pointer to the starting address for the block of memory so, (2) it can be freed when it is no longer needed.
It is imperative that you use a memory error checking program to insure you do not attempt to access memory or write beyond/outside the bounds of your allocated block, attempt to read or base a conditional jump on an uninitialized value, and finally, to confirm that you free all the memory you have allocated.
For Linux valgrind is the normal choice. There are similar memory checkers for every platform. They are all simple to use, just run your program through it.
$ valgrind ./bin/stack_ll
==25935== Memcheck, a memory error detector
==25935== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==25935== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info
==25935== Command: ./bin/stack_ll
==25935==
Top Element is 10
popped element is 10
popped element is 9
popped element is 8
popped element is 7
popped element is 6
popped element is 5
popped element is 4
popped element is 3
popped element is 2
popped element is 1
popped element is 0
stack is empty
==25935==
==25935== HEAP SUMMARY:
==25935== in use at exit: 0 bytes in 0 blocks
==25935== total heap usage: 12 allocs, 12 frees, 184 bytes allocated
==25935==
==25935== All heap blocks were freed -- no leaks are possible
==25935==
==25935== For counts of detected and suppressed errors, rerun with: -v
==25935== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
Always confirm that you have freed all memory you have allocated and that there are no memory errors.
If you have any further questions, just let me know.