C Program to Implement Circular Queue..

#include<stdio.h>
#define maxi 5

struct circularqueue // Structure of Circular Queue...
{
 int a[maxi];
 int f,r;
};

void insert(struct circularqueue *p,int x);
int delete(struct circularqueue *p);
void display(struct circularqueue q);

int flag;      // Temporary variable to handle the error condition in delete function...

void main()
{
 struct circularqueue c;
 c.f=c.r=-1;
 printf("Empty Queue is Created..");
 int ch;
 int temp=0;       // Temporary variable to exit the menu driven program...
 printf("\nChoice : 1) Insertion 2) Deletion 3) Display Queue 4) Stop");
 while(1){
 printf("\nEnter your choice..");
scanf("%d",&ch);
 switch(ch){
  case 1:
          {
            int x;
           printf("\nEnter the element to be inserted..");
           scanf("%d",&x);
           insert(&c,x);
           break;
          }
  case 2:
         {
           flag=0;
           int t=delete(&c);
           if(flag==0)
           printf("\nThe Element which is deleted is..%d",t);
           break;
         }
  case 3:{ display(c); break;}
  case 4:{ temp=1; break; }
  default: { printf("\nPlease enter a valid choice.."); }
 }
 if(temp==1)
  break;
}
}

void insert(struct circularqueue *p,int x)
{
 if((p->f==0&&p->r==maxi-1)||(p->r==p->f-1)){  // Corner case to handle if the queue is full...
 printf("\nQueue Overflow..");
 return;
 }
else if(p->f==-1&&p->r==-1){ // Corner case to handle if the queue is empty...
  p->f=p->r=0;
  p->a[p->f]=x;
 }
 else{
  p->r=(p->r+1)%maxi;
  p->a[p->r]=x;
 }
}

int delete(struct circularqueue *p)
{
 int x;
 if(p->f==-1&&p->r==-1){   // Corner case to handle if the queue is empty...
 printf("\nCircular Queue is Empty..");
 flag=1;
 }
 else if(p->f==p->r){  // Corner case to handle if the queue contains a single element...
  x=p->a[p->f];
  p->f=p->r=-1;
 }
 else{
  x=p->a[p->f];
  p->f=(p->f+1)%maxi;
}
 return x;
}

void display(struct circularqueue q)
{
  if(q.f==-1&&q.r==-1){   // Corner case to handle if the queue is empty...
   printf("\nThe Queue is Empty..");
   return;
  }
  printf("\nThe Queue is..");
  while(q.f!=-1){     // Deleteting all the nodes of the local circular queue and displaying all the elements...
   printf(" %d",delete(&q));
  }
}

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