Queue Implementation in C

#include stdio.h
#include stdlib.h

int front = -1, back = -1, q[5];

void push(int value)
{
  if(back>5)
  {
    printf("Queue is full");
  }

  if (front = -1)
  {
    front++;
  }

  back++;
  q[back] = value;
}

void pop()
{
  if (front > back || (front == -1 && back == -1))
  {
    printf("Queue is empty.");
    front = -1;
    back = -1;
  }
  else
  {
    printf("\n%d is deleted", q[front]);
    front++;
  }
}

void display()
{
  if (front == -1 && back == -1)
  {
    printf("Queue is empty");
  }
  else
  {
    for (int i = front; i <= back; i++)
    {
      printf("\n%d ", q[i]);
    }
  }
}

void main()
{
  int value, choice;

  while (1)
  {
    printf("\nSELECT YOUR CHOICE::\n1.INSERT ELEMENT \n2.DELETE ELEMENT \n3.DISPLAY\n4.EXIT.");
    scanf("%d", &choice);

    switch (choice)
    {
    case 1:
    {
      printf("Enter 5 Elements:");
      for (int i = 0; i <= 4; i++)
      {
        scanf("%d", &q[i]);
        push(q[i]);
      }
      break;
    }
    case 2:
      pop();
      break;
    case 3:
      display();
      break;
    case 4:
      exit(0);
    default:
      printf("Enter Choice between 1 to 4");
    }
  }
}