implementing stack with linked list in 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

codaddict · Accepted Answer · 2012-05-17 11:39:23Z

2

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.

edited May 17, 2012 at 11:39

answered May 17, 2012 at 10:17

codaddict

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2 Comments

nain33 Over a year ago

Thanks a lot, a lot more problems than I realised but fixed now thanks to you.

Jay Over a year ago

There is no I in stack or overflow :)

Community · Accepted Answer · 2017-05-23 11:58:24Z

1

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?

edited May 23, 2017 at 11:58

CommunityBot

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answered May 17, 2012 at 10:27

hmjd

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Comments

Quest · Accepted Answer · 2015-10-02 18:35:16Z

0

#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;
}

edited Oct 2, 2015 at 18:35

Quest

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answered Oct 2, 2015 at 17:44

Rajesh Kharche

1

2 Comments

mpromonet Over a year ago

How this answer to the question ?

JAL Over a year ago

While this code may answer the question, providing additional context regarding why and/or how this code answers the question improves its long-term value.

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