C program for FCFS CPU scheduling algorithm

Introduction to FCFS :

                     By far the simplest CPU-scheduling algorithm is the first-come, first-served (FCFS) scheduling algorithm. With this scheme, the process that requests the CPU first is allocated the CPU first. The implementation of the FCFS policy is easily managed with a FIFO queue.When a process enters the ready queue,its PCB is linked onto the tail of the queue. When the CPU is free, it is allocated to the process at the head of the queue.The running process is then removed from the queue. The code for FCFS scheduling is simple to write and understand.


C program for FCFS scheduling :

#include<stdio.h>
int main()
{
int process[10],arrival[10],exec[10],start[10],end[10],wait[10],turnaround[10];
int n,i,j,temp,totalwait=0,totalturn=0;
float avgwait,avgturn;
printf("Enter the number of processes\n");
scanf("%d",&n);
printf("Enter the process name,arrival time and execution time of each process\n");
for(i=0;i<n;i++)
scanf("%d%d%d",&process[i],&arrival[i],&exec[i]);
for(i=0;i<n-1;i++)
{
for(j=i+1;j<n;j++)
{
if(arrival[i]>arrival[j])
{
temp=arrival[i];
arrival[i]=arrival[j];
arrival[j]=temp;
temp=process[i];
process[i]=process[j];
process[j]=temp;
temp=exec[i];
exec[i]=exec[j];
exec[j]=temp;
}
}
}
printf("Process name\tArrival time\tExecution time\n");
for(i=0;i<n;i++)
printf("%d\t\t%d\t\t%d\n",process[i],arrival[i],exec[i]);
start[0]=arrival[0];
end[0]=arrival[0]+exec[0];
wait[0]=0;
turnaround[0]=exec[0];
totalturn+=turnaround[0];
for(i=1;i<n;i++)
{
if(arrival[i]<=end[i-1])
start[i]=end[i-1];
else
start[i]=arrival[i];
wait[i]=start[i]-arrival[i];
totalwait+=wait[i];
end[i]=start[i]+exec[i];
turnaround[i]=exec[i]+wait[i];
totalturn+=turnaround[i];
}
avgwait=(float)totalwait/(float)n;
avgturn=(float)totalturn/(float)n;
printf("Process name\tArrival time\tExecution time\tStart time\tEnd time\tWaiting                                            time\tTurnaround time\n");
for(i=0;i<n;i++)
printf("%d\t\t%d\t\t%d\t\t%d\t\t%d\t\t%d\t\t%d\n",process[i],arrival[i],exec[i],start[i],
                       end[i],wait[i],turnaround[i]);
printf("Total waiting time is %d\n",totalwait);
printf("Average waiting time is %f\n",avgwait);
printf("Total turnaround time is %d\n",totalturn);
printf("Average turnaround time is %f\n",avgturn);
return 0;

}


OUTPUT :