Data structures using C,
Write a C Program to implement Priority Queue using structure.
Priority QUEUE is a abstract data type in which the objects are inserted with respect to certain priority. In this program, we created the simple ascending order priority queue using the structure, here items are inserted in ascending order. Structure is a c composite data type, in which we can define all the data types under the same name or object.Read more about C Programming Language .

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#define SIZE 5            /* Size of Queue */
int f=0,r=-1;       /* Global declarations */
typedef struct PRQ
{
 int ele;
 int pr;
}PriorityQ;

PriorityQ PQ[SIZE];

PQinsert(int elem, int pre)
{
 int i;       /* Function for Insert operation */
 if( Qfull()) printf("nn Overflow!!!!nn");
 else
 {
  i=r;
  ++r;
  while(PQ[i].pr >= pre && i >= 0) /* Find location for new elem */
  {
   PQ[i+1]=PQ[i];
   i--;
  }
  PQ[i+1].ele=elem;
  PQ[i+1].pr=pre;
 }
}

PriorityQ PQdelete()
{                      /* Function for Delete operation */
 PriorityQ p;
 if(Qempty()){ printf("nnUnderflow!!!!nn");
 p.ele=-1;p.pr=-1;
 return(p); }
 else
 {
  p=PQ[f];
  f=f+1;
  return(p);
 }
}

int Qfull()
{                     /* Function to Check Queue Full */
 if(r==SIZE-1) return 1;
 return 0;
}

int Qempty()
{                    /* Function to Check Queue Empty */
 if(f > r) return 1;
 return 0;
}

display()
{                  /* Function to display status of Queue */
 int i;
 if(Qempty()) printf(" n Empty Queuen");
 else
 {
  printf("Front->");
  for(i=f;i<=r;i++)
   printf("[%d,%d] ",PQ[i].ele,PQ[i].pr);
  printf("<-Rear");
 }
}

main()
{                         /* Main Program */
 int opn;
 PriorityQ p;
 do
 {
  clrscr();
  printf("n ### Priority Queue Operations(DSC order) ### nn");
  printf("n Press 1-Insert, 2-Delete,3-Display,4-Exitn");
  printf("n Your option ? ");
  scanf("%d",&opn);
  switch(opn)
  {
  case 1: printf("nnRead the element and its Priority?");
  scanf("%d%d",&p.ele,&p.pr);
  PQinsert(p.ele,p.pr); break;
  case 2: p=PQdelete();
  if( p.ele != -1)
   printf("nnDeleted Element is %d n",p.ele);
  break;
  case 3: printf("nnStatus of Queuenn");
  display(); break;
  case 4: printf("nn Terminating nn"); break;
  default: printf("nnInvalid Option !!! Try Again !! nn");
  break;
  }
  printf("nnnn  Press a Key to Continue . . . ");
  getch();
 }while(opn != 4);
}

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