RoundRobin Program of practical slip

 /* Implementation of RoundRobin method for CPU scheduling using Circular LL */
 


#include<stdlib.h>
#define newnode (struct node *)malloc(sizeof(struct node))
struct node
{ int jobno,time;
  struct node *next;
}*JOBQ=NULL;


void erase()
{ struct node *S,*T;
  if(JOBQ!=NULL)
  { for(T=JOBQ;T->next!=JOBQ; T=T->next) ;  // go to last node
    T->next=NULL;

    while(JOBQ!=NULL)  { S=JOBQ;  JOBQ=JOBQ->next;  free(S);  }
  }
}

void CreateJOBQ()
{ struct node *S;   int i,n;
  printf("\nHow many jobs?"); scanf("%d",&n);


  if(JOBQ!=NULL) erase(JOBQ);
  JOBQ=newnode;
  printf("\nEnter JOB No. & execution time in sec. "); scanf("%d %d",&JOBQ->jobno,&JOBQ->time);

  S=JOBQ;
  for(i=2;i<=n;i++)
  { S->next=newnode;
    S=S->next;
    printf("\nEnter JOB No. & execution time in sec. "); scanf("%d %d",&S->jobno,&S->time);
  }
  S->next=JOBQ;
}

void DisplayJOBQ()
{struct node *T=JOBQ;
  if(JOBQ==NULL) printf("\nJOB Q is Empty!");
  else
  { printf("\nJOB  Rem. Time");
    do{ printf("\n J%d : %d ",T->jobno,T->time);
    T=T->next;
      }while(T!=JOBQ);
  }
}

void ExecuteJOBQ()
{ struct node *T=JOBQ,*S=NULL,*t1;  int flag,timeslot=1,time=0; char choice;
  printf("\nEnter Time Slot (in sec.) "); scanf("%d",&timeslot);
  printf("\nclock CPU   JOBQ ");
  while(JOBQ!=NULL)
  {
    do{ flag=0;
    if(T->time<=timeslot)  // job remaining time < time slot
    { printf("\n%3d  J%d(%d) |--",time,T->jobno,T->time); // cpu allocated
      for(t1=T->next; t1!=T; t1=t1->next) printf(" J%d(%d) ",t1->jobno,t1->time);  // print JOBQ
      time+=T->time; // increment clock
      T->time=0; // job finished, delete from JOBQ
      if(T==JOBQ) // 1st job
      { if(JOBQ->next==JOBQ) // only 1 job in Q
        { JOBQ=NULL; free(T); T=NULL; } // JOBQ became empty
        else  // more jobs in Q
        {  for(t1=JOBQ;t1->next!=JOBQ; t1=t1->next) ;  // go to last node
           JOBQ=JOBQ->next;   t1->next=JOBQ;
           free(T);     T=JOBQ; flag=1;
        }
      }
      else // job other than 1st position
      {   S->next=T->next; free(T);  T=S->next;
      }

    }
    else  // job is executed for given time slot
    {  printf("\n%3d  J%d(%d) |--",time,T->jobno,T->time); // cpu allocated
       for(t1=T->next; t1!=T; t1=t1->next) printf(" J%d(%d) ",t1->jobno,t1->time); // print JOBQ

       T->time-=timeslot;
       time+=timeslot;
       S=T; T=T->next;  // go to next job
    }

    printf(" --|  Add New Job(y/n)? ");  choice=getche();
    if(choice=='y' || choice=='Y')
    { struct node *S1;
      if(JOBQ==NULL) // JOBQ empty
      { JOBQ=newnode; JOBQ->next=JOBQ;    // 1st job in Q
        printf("\nEnter JOB No. & execution time in sec. "); scanf("%d %d",&JOBQ->jobno,&JOBQ->time);
        T=JOBQ; flag=1;
      }
      else
      { for(S1=S;S1->next!=S; S1=S1->next) ;  // go to last node of JOBQ
        S1->next=newnode; S1=S1->next; S1->next=S;    // add new job at the end of JOBQ
        printf("\nEnter JOB No. & execution time in sec. "); scanf("%d %d",&S1->jobno,&S1->time);
      }
    }
      }while(T!=JOBQ || flag);
  }
  printf("\n%3d  -idle-",time);
}

char menu()
{ char choice='a';
  clrscr();
  printf("----- Round Robin ------");
  printf("\nC: Create New JOB Queue");
  printf("\nD: Display JOB Queue");
  printf("\nE: Execute JOB Queue");
  printf("\nX: exit");
  printf("\nEnter your choice : ");
  choice=getche();
  return toupper(choice);
}

void main()
{
  while(1)
  { switch(menu())
    { case 'X' : erase(); exit(0);  // release memory allocated to JOBQ
      case 'C' : CreateJOBQ();  break;
      case 'D' : DisplayJOBQ(); break;
      case 'E' : ExecuteJOBQ(); break;
      default  : printf("\7 Invalid Choice!");
    }
    printf("\npress any key to continue...");
    getch();
  }

}