Round Robin CPU Scheduling - C Program - Operating Systems

/* Round Robin algorithm for CPU scheduling ( considering arrival time  and maintains a queue
as well)
Ref. Operating Systems by william stallings */

#include<stdio.h>
struct process
{
char name;
int at,bt,wt,tt,rt;
int completed;
float ntt;
}p[10];
int n;
int q[100];  //queue
int front=-1,rear=-1;
void enqueue(int i)
{
if(rear==100)
{
printf("overflow");
return 0;
}rear++;
q[rear]=i;
if(front==-1)
front=0;

}

int dequeue()
{
if(front==-1)
{
printf("underflow");
return 0;
} int temp=q[front];
if(front==rear)
front=rear=-1;
else
front++;
return temp;
}
int isInQueue(int i)
{int k;
for(k=front;k<=rear;k++)
{
if(q[k]==i)
return 1;
}
return 0;

}void sortByArrival()
{
struct process temp;
int i,j;
for(i=0;i<n-1;i++)
for(j=i+1;j<n;j++)
{
if(p[i].at>p[j].at)
{
temp=p[i];
p[i]=p[j];
p[j]=temp;
}
}
}

void main()
{
int i,j,time=0,sum_bt=0,tq;
char c;
        float avgwt=0;
 printf("Enter no of processes:");
 scanf("%d",&n);
 for(i=0,c='A';i<n;i++,c++)
 {
 p[i].name=c;
 printf("\nEnter the arrival time and burst time of process %c: ",p[i].name);
 scanf("%d%d",&p[i].at,&p[i].bt);
 p[i].rt=p[i].bt;
 p[i].completed=0;
 sum_bt+=p[i].bt;

}

printf("\nEnter the time quantum:");
scanf("%d",&tq);

sortByArrival();
enqueue(0);          // enqueue the first process
printf("Process execution order: ");
for(time=p[0].at;time<sum_bt;)       // run until the total burst time reached
{   i=dequeue();

if(p[i].rt<=tq)
{                          // for processes having remaining time with less than or equal time quantum
                     
time+=p[i].rt;
p[i].rt=0;
p[i].completed=1;        
   printf(" %c ",p[i].name);
            p[i].wt=time-p[i].at-p[i].bt;
            p[i].tt=time-p[i].at;    
            p[i].ntt=((float)p[i].tt/p[i].bt);
            for(j=0;j<n;j++)                // enqueue the processes which have come while scheduling
            {
            if(p[j].at<=time && p[j].completed!=1&& isInQueue(j)!=1)
            {
            enqueue(j);
           
            }
           }
        }
   else               // more than time quantum
   {
    time+=tq;
    p[i].rt-=tq;
    printf(" %c ",p[i].name);
    for(j=0;j<n;j++)             //enqueue the processes which have come scheduling first
            {
            if(p[j].at<=time && p[j].completed!=1&&i!=j&& isInQueue(j)!=1)
              {
            enqueue(j);
           
            }
           }
           enqueue(i);   // then enqueue the uncompleted process
         
   }

 
 
}

printf("\nName\tArrival Time\tBurst Time\tWaiting Time\tTurnAround Time\t Normalized TT");
for(i=0;i<n;i++)
{avgwt+=p[i].wt;
printf("\n%c\t\t%d\t\t%d\t\t%d\t\t%d\t\t%f",p[i].name,p[i].at,p[i].bt,p[i].wt,p[i].tt,p[i].ntt);
}
printf("\nAverage waiting time:%f\n",avgwt/n);
}


     


 OUTPUT:
Enter no of processes:5

Enter the arrival time and burst time of process A: 0 3

Enter the arrival time and burst time of process B: 2 6

Enter the arrival time and burst time of process C: 4 4

Enter the arrival time and burst time of process D: 6 5

Enter the arrival time and burst time of process E: 8 2

Enter the time quantum:4
Process execution order:  A  B  C  D  B  E  D
Name    Arrival Time    Burst Time      Waiting Time    TurnAround Time  Normalized TT
A               0                              3              0                           3                 1.000000
B               2                             6               9                           15                 2.500000
C               4                             4               3                            7                  1.750000
D               6                             5               9                          14                 2.800000
E               8                             2               9                           11                 5.500000
Average waiting time:6.000000

--------------------------------
Process exited after 16.79 seconds with return value 31
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