C-Program to implement linear queue operations

Program

#include<stdio.h>
void insertion(int);
void deletion();
void printing();
int q[20],f,r,max;
f=0,r=0,max=5;
main()
{
 int x,ch;
 while(1)
 {
  printf("Type 1 go for insertion");
  printf("\nType 2 go for deletion");
  printf("\nType 3 go for printing");
  printf("\nType 4 go for exit");
  printf("\nEnter choice");
  scanf("%d",&ch);
  switch(ch)
  {
   case 1:
   {
    printf("Enter Data");
    scanf("%d",&x);
    insertion(x);
    break;
   }
   case 2:
   {
    deletion();
    break;
   }
   case 3:
   {
    printing();
    break;
   }
   case 4:
   {
    exit();
    break;
   }
  }
 }
}

void insertion(int x)
{
 if(r>max)
 {
  printf("Queue is overflow");
  exit(0);
 }
 else
 {
  r=r+1;
  q[r]=x;
 }
 if(f==0)
 f=1;
}

void deletion()
{
 if(f==0)
 {
  printf("Queue is overflow");
  exit(0);
 }
 if(f==r)
 {
  f=0;
  r=0;
 }
 else
 f=f+1;
}
void printing()
{
 int i=0;
 for(i=f;i<=r;i++)
 printf("%d",q[i]);
}