Shortest Job First (SJF)

Operating Systems Lab Manual / Shortest Job First (SJF)

Program Name	Write a C Program for CPU scheduling algorithm Shortest Job First (SJF)
Theory	In Shortest Job First (SJF) the process whose job takes less time it will be served first by the processor. The processor gets processes from the ready Queue. 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 p[20], bt[20], wt[20], tat[20], i, k, n, temp; float wtavg, tatavg; printf("\nEnter number of processes: "); scanf("%d", &n); for(i=0;i<n;i++) { p[i]=i; printf("Enter Burst Time for Process %d: ", i); scanf("%d", &bt[i]); } for(i=0;i<n;i++) for(k=i+1;k<n;k++) if(bt[i]>bt[k]) { temp=bt[i]; bt[i]=bt[k]; bt[k]=temp; temp=p[i]; p[i]=p[k]; p[k]=temp; } 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", p[i], bt[i], wt[i], tat[i]); printf("\nAverage Waiting Time: %f", wtavg/n); printf("\nAverage Turnaround Time: %f", tatavg/n); getch(); }
Input	Enter number of processes: 4 Enter Burst Time for Process 0: 3 Enter Burst Time for Process 1: 6 Enter Burst Time for Process 2: 7 Enter Burst Time for Process 3: 8
Output	Process burst Time Waiting Time Turnaround Time P0 3 0 3 P1 6 3 9 P2 7 9 16 P3 8 16 24 Average Waiting Time: 7.000000 Average Turnaround Time: 13.000000

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