//STACK PROGRAM
/*
#include <stdio.h>
#include <stdbool.h>
#define SIZE 5
//stack implemented using array, LIFO

//stack_init(): Make stack empty
//empty(): return true if stack is empty, false if otherwise
//push(val): add val to stack
//pop(): remove top item
//top(): return top item, do not remove

//input positive number will push to stack
//input negative number will invoke top()
//input 0 will invoke pop()

int stack[SIZE],t,input;

void stack_init(void);
bool empty(void);
bool push(int);
void pop(void);
int top(void);
bool isFull(void);

int main(void) {
  printf("Hello World\n");
  stack_init();

  while(1){

    printf("input:");
    scanf("%d",&input);
    if(input>0){
      if(push(input)){
        //printf("pushed!\n");
      }else{
        printf("array is full!\n");
      }
    }else if(input<0){
      if(top()!=-1) printf("output: %d\n", top());
      else printf("Error - Stack is empty\n");
    }else pop();
  }
  return 0;
}

void stack_init(){
  t = -1;
}

bool empty(){
  if (t == -1) return true;
  else return false;
}

bool push(int val){
  if(isFull()){
    return false;
  }else{
    t=t+1;
    stack[t]=val;
    return true;
  }
}

void pop(){
  if(!empty()) t=t-1;
  else printf("Error - Stack is empty\n");
}

int top(){
  if(!empty()) return stack[t];
  else return -1;
}

bool isFull(){
  if (t==SIZE){
    return true;
  }else{
    return false;
  }
}
*/



//QUEUE PROGRAM
#include <stdio.h>
#include <stdbool.h>
#define SIZE 4

//queue_init():makes queue empty
//empty:return true if queue is empty
//enqueue(val):add val into queue
//dequeue():remove first item FIFO
//front(): return front item, do not remove

//input positive invoke enqueue
//input negative invoke front
//input 0 invoke dequeue

int data[SIZE],r,f,input;

void queue_init(void);
bool empty(void);
bool enqueue(int);
void dequeue(void);
int front(void);
int rear(void);

int main(void) {
  printf("Hello world!\n");
  queue_init();

  while(1){
    printf("input:");
    scanf("%d",&input);
      if(input>0){
        if(enqueue(input)){
          //printf("enqueued!\n");
        }else{
          printf("array is full!");
        }

      }else if(input<0){
        if(front()==-42){
          printf("Error - Queue is empty\n");
        }else{
          printf("f:%d\n",front());
          printf("r:%d\n",rear());
        }
      }else{
        dequeue();
      }
  }
  return 0;
}

void queue_init(){
  r = f = -1;
}

bool empty(){
  if (r==-1 && f==-1){
    return true;
  }else{
    return false;
  }
}

bool enqueue(int val){
  if(((r+1)==f)||((r==SIZE-1)&&(f==0))){
    return false;
  }else{
    if(empty()){
      r=0;
      f=0;
    }else{
      r=r+1;
      if(r==SIZE){
        r=0;
      }
    }
    //printf("f:%d,r:%d",f,r);
    data[r]=val;
    return true;
  }
}

void dequeue(){
  if(!empty()){
    if(r==f){
      r=f=-1;
    }else{
      f=f+1;
      if(f==SIZE){
        f=0;
      }
    }
  }else{
    printf("Error - Queue is empty\n");
  }
}

int front(){
  if(!empty()){
    return data[f];
  }else{
    return -42;
  }
}

int rear(){
  if(!empty()){
    return data[r];
  }else{
    return -43;
  }
}