StackUsingArray.c

struct Stack {
  int a[5];
  int t;
};

struct Stack* create() {
  struct Stack* s = malloc(sizeof(struct Stack));
  s -> t = 0;
  return s;
}

void dropStack(struct Stack* s) {
  free(s);
}

// needs overflow checking
void push(Struct stack s, int val) {
  s->a[s->t] = val;
  s->t ++;
}

// needs underflow checking
int pop(struct Stack* s) {
  int val = s->a[s->t];
  s->t--;
  return val;
}