implementing stack with linked list in C - c

Question

I'm having trouble implementing a Stack using a linked list with struct. The program compiles fine but when I run it, it prints the first element but then reads the next node as a NULL. I think it might be an error with my passing of the stack to the push method but I am not sure and I have not been successful in fixing it so I'm asking for your help:
#include <stdio.h>
#include <stdlib.h>
struct stackNode{
char data;
struct stackNode *nextPtr;
};
typedef struct stackNode StackNode;
typedef StackNode *StackNodePtr;
void convertToPostfix(char infix[], char postfix[]);
int isOperator(char c);
int precedence(char operator1, char operator2);
void push(StackNodePtr *topPtr, char value);
char pop(StackNodePtr *topPtr);
char stackTop(StackNodePtr topPtr);
int isEmpty(StackNodePtr topPtr);
void printStack(StackNodePtr topPtr);
int main(){
convertToPostfix(NULL, NULL);
return 0;
}
void convertToPostfix(char infix[], char postfix[]){
StackNode stack = {'(', NULL};
StackNodePtr stackPtr = &stack;
push(stackPtr, 'a');
//printf("%s\n", stackPtr->data);
printStack(&stack);
}
void push(StackNodePtr *topPtr, char value){
StackNode *node;
node=(StackNodePtr)malloc(sizeof(StackNodePtr));
node->data=value;
node->nextPtr=*topPtr;
*topPtr=node;
}
void printStack(StackNodePtr topPtr){
if(topPtr == NULL){
printf("%s\n", "NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO");
return;
}
printf("%c\n", topPtr->data);
printStack(topPtr->nextPtr);
}
Any help would be appreciated.
Thanks

Answer 1

Several problems I could see:
1) printStack(&stack); should be printStack(stackPtr); as you are passing address of stackPtr to the push function.
2)
node = (StackNodePtr)malloc(sizeof(StackNodePtr));
should be:
node = malloc(sizeof(StackNode));
3)
push(stackPtr, 'a');
should be:
push(&stackPtr, 'a');
As you need to pass the address of the top pointer.

Answer 2

This is incorrect:
node=(StackNodePtr)malloc(sizeof(StackNodePtr));
as it is only allocating memory for a struct stackNode* (commonly 4-bytes for any pointer type), when it should be allocating memory for a struct stackNode (at least 5 bytes):
node = malloc(sizeof(StackNode));
--
See Do I cast the result of malloc?

Answer 3

#include <stdio.h>
#include <stdlib.h>
struct node {
int data;
struct node * link;
};
void push(struct node **, int);
int pop(struct node **);
void display(struct node *);
void printMenu();
int main() {
struct node * p;
p = NULL;
int data, ch, data1;
//char choice[10];
do {
printMenu();
printf("Enter your choice\n");
scanf("%d", &ch);
switch (ch) {
case 1:
printf("Enter the element to be pushed\n");
scanf("%d", &data);
push(&p, data);
break;
case 2:
data1 = pop(&p);
if (data1 != -1000)
printf("The popped element is %d\n", data1);
break;
case 3:
printf("The contents of the stack are");
display(p);
printf("\n");
break;
default:
return 0;
}
} while (1);
return 0;
}
void printMenu() {
printf("Choice 1 : Push\n");
printf("Choice 2 : Pop\n");
printf("Choice 3 : Display\n");
printf("Any other choice : Exit\n");
}
void push(struct node **q, int num) {
struct node *temp;
temp = (struct node *)malloc(sizeof(struct node));
temp->link = (*q);
temp->data = num;
(*q) = temp;
}
void display(struct node *q) {
//Fill in the code here
struct node *temp = q;
if (temp == NULL)
printf(" {}");
while (temp != NULL)
{
printf(" %d", temp->data);
temp = temp->link;
}
}
int pop(struct node **q) {
//Fill in the code here
struct node *temp;
int item;
if (*q == NULL)
{
printf("Stack is empty\n");
return -1000;
}
temp = *q;
item = temp->data;
*q = (*q)->link;
free(temp);
return item;
}