i'm still beginning to learn c so please bear with me. i'm trying to create a postfix calculator using linked-list. when i compile, it doesn't show any errors but when it's executed it would show Segmentation Fault. i don't know how to deal with this, please help. here's my code:

Code:



	
Code:

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


    typedef struct node	{
	    int num;
	    struct node *next;
    } node;


    void push(int num, node **head);
    int pop(node **head);
    void display(node **head);
    int is_empty();
    int evaluatePostfix();
    
    struct node *head;


    int main()	{
	    head = NULL;
        char exp[1000]; // = "5 1 2 + 4 * + 3 -";
	    printf("Input expression:\t");
    	fgets(exp, 1000, stdin);
    	for(int i = 1; i <= strlen(exp); i++) {
    		if(exp[i] == '\n') {
    			exp[i] = '\0';
    		}
    		else if (exp[0] == '\n') {
				printf("stack is empty\n");
				exit(0);
	    	}
    	}
	    printf("%s = %d\n", exp, evaluatePostfix(exp));
    
    	return 0;
}




    int evaluatePostfix(char* exp)	{
	    char * token;
    	int counter = 0;
    	char temp[256][256];
    	token = strtok(exp, " ");
    	while(token != NULL)	{
    		strcpy(temp[counter], token);
    		token = strtok(NULL, " ");	
			counter++;
	    }
		
    	for (int i = 0; i < counter; i++)	{
    		if (isdigit(*(temp[i]))) {
    			int val = atoi(temp[i]);
                push(val, &head);
	    	}
            else   {
    			int val1 = pop(&head);
                int val2 = pop(&head);
                switch (exp[i])	{
	    			case '+':    push(val2 + val1, &head);
	    			    	     printf("%d\n", (*head).num);
				                 break;
			    	case '-':    push(val2 - val1, &head);    break;
			    	case '*':    push(val2 * val1, &head);    break;
			    	case '/':    push(val1 / val2, &head);    break;
			    }
		    }
        }
        return pop(&head);
    }




    void push (int item, node **head) {
    	node *temp;
    	node * get_node(int);
    	temp = get_node(item);
    	temp->next = *head;
    	*head = temp;
    }


    node *get_node(int item) {
    	node *temp;
    	temp = (node*)malloc(sizeof(node));
    	if (temp == NULL)
    		printf("\nMemory cannot be allocated");
    	temp->num = item;
	    temp->next = NULL;
    	return(temp);
    }




    int pop(node **head)	{
    	int item;
    	node *temp;
    	item = (*head)->num;
        temp = *head;
    	*head = (*head)->next;
    	free(temp);
    	return(item);
    }
	
    int is_empty(node *temp) {
    	if (temp == NULL)
    		return 1;
    	else
	    	return 0;
    }




    void display(node **head)	{
    	node *temp;
    	temp = *head;
    	if(head == NULL)	{
    		printf("stack is empty\n");
    		return;
    	}
    	printf("\n");
	    printf("=========\n");
    	while(temp!=NULL)	{
    		printf("%d\n", (*temp).num);
    		temp = (*temp).next;
    	}
    	printf("=========\n");
    }