#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct {
  int top;
  int capacity;
  char *array;
} stack;

stack *createStack(int c) {
  stack *Stack = (stack *)malloc(sizeof(stack));
  if (!Stack) {
    return NULL;
  }
  Stack->capacity = c;
  Stack->top = -1;
  Stack->array = (char *)malloc(Stack->capacity);
  if (!Stack->array) {
    free(Stack);
    return NULL;
  }
  return Stack;
}

bool isfull(stack *s) { return s->top == s->capacity - 1; }
bool isempty(stack *s) { return s->top == -1; }

int push(stack *s, char v) {
  if (isfull(s)) {
    printf("stack overflow");
    return -1;
  }
  s->array[++s->top] = v;
  return s->top;
}
int pop(stack *s) {
  if (isempty(s)) {
    printf("empty");
    return -1;
  }
  return s->array[s->top--];
}

void display(stack *s) {
  for (int i = 0; i <= s->top; i++) {
    printf("%c", s->array[i]);
  }
}

int main() {
  stack *ms = createStack(3);

  push(ms, 'a');
  push(ms, 'b');
  display(ms);
}