// import modules
#include <stdio.h>
#include <limits.h>
#include <stdlib.h>

// define Stack struct
struct Stack {
        int* arr;
        int top;
        unsigned length;
};

// create stack function
struct Stack* createStack(unsigned len) {
        // create stack
        struct Stack* stack = (struct Stack*) malloc(sizeof(struct Stack));

        // insert values
        stack->length = len;
        stack->top = -1;
        stack->arr = (int*)malloc(stack->length * sizeof(int));

        // return stack
        return stack;
}

// check stack is full
int isFull(struct Stack* stack) {
        // check full
        return stack->top == stack->length - 1;
}

// check stack is empty
int isEmpty(struct Stack* stack) {
        // check empty
        return stack->top == -1;
}

// push item into the stack
int push(struct Stack* stack, int i) {
        // check stack is full
        if (isFull(stack)) {
                return 0;
        }

        // insert item
        stack->arr[++stack->top] = i;

        // return top index
        return stack->top;
}

// pop from stack
int pop(struct Stack* stack) {
        // check stack is empty
        if (isEmpty(stack)) {
                return 0;
        }

        // return top value
        return stack->arr[stack->top--];
}

// main
int main(void) {
        // create a stack
        struct Stack* stack = createStack(100);

        // push items
        push(stack, 10);
        push(stack, 20);
        push(stack, 30);

        // print length
        printf("length: %d\n", stack->length);

        // pop item
        printf("pop: %d\n", pop(stack));

        return 0;
}