/*
CSE 303, Spring 2009, Marty Stepp
This program creates a simple stack of ints and provides a text UI
for pushing, popping, and clearing the stack.
This program is intended to practice manipulating linked data structures in C.
*/

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

/* A struct type to represent individual nodes in a linked stack. */
typedef struct Node {
    int data;
    struct Node* next;
} Node;

int main(void) {
    int choice;
    Node* stack;   // pointer to top of stack
    
    while (1) {
        printf("(1) push, (2) pop, (3) clear, or (0) quit? ");
        scanf("%d", &choice);
        if (choice == 1) {
            // push
            Node* oldFront = stack;
            stack = (Node*) malloc(sizeof(Node));
            printf("Number to push? ");
            scanf("%d", &stack->data);
            stack->next = oldFront;
        } else if (choice == 2) {
            // pop
            if (stack) {
                Node* oldFront = stack;
                printf("%d\n", stack->data);
                stack = stack->next;
                free(oldFront);
            }
        } else if (choice == 3) {
            // clear
            while (stack) {
                Node* oldFront = stack;
                stack = stack->next;
                free(oldFront);
            }
        } else {
            // quit
            break;
        }
    }
    
    return 0;
}