First Come First Serve (FCFS)

Operating Systems Lab Manual / First Come First Serve (FCFS)

Program Name	Write a C Program for CPU scheduling algorithm for First Come First Serve (FCFS)
Theory	In First Come First Serve (FCFS) the process which comes first will be served first by the processor. The processor gets processes from the ready Queue. In FCFS we calculate average waiting time of all the processes. Waiting time (n) = waiting time (n-1) + Burst time (n-1) Turnaround time (n)= waiting time(n)+Burst time(n) Average waiting time = Total waiting Time / Number of process. Average Turnaround time = Total Turnaround Time / Number of process
Program	#include<stdio.h> #include<conio.h> void main() { int bt[20], wt[20], tat[20], i, n; float wtavg, tatavg; printf("\n Enter number of processes:"); scanf("%d", &n); for(i=0;i<n;i++) { printf("\nEnter Burst Time for Process %d:", i); scanf("%d", &bt[i]); } wt[0] = wtavg = 0; tat[0] = tatavg = bt[0]; for(i=1;i<n;i++) { wt[i] = wt[i-1] +bt[i-1]; tat[i] = tat[i-1] +bt[i]; wtavg = wtavg + wt[i]; tatavg = tatavg + tat[i]; } printf("\t Process \t burst Time \t Waiting Time \t Turnaround Time\n"); for(i=0;i<n;i++) printf("\n\t P%d \t\t %d \t\t %d \t\t %d", i, bt[i], wt[i], tat[i]); printf("\n Average Waiting Time: %f", wtavg/n); printf("\n Average Turnaround Time: %f", tatavg/n); getch(); }
Input	Enter number of processes:3 Enter Burst Time for Process 0:24 Enter Burst Time for Process 1:3 Enter Burst Time for Process 2:3
Output	Process burst Time Waiting Time Turnaround Time P0 24 0 24 P1 3 24 27 P2 3 27 30 Average Waiting Time: 17.000000 Average Turnaround Time: 27.000000

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