Write the simulation program for preemptive scheduling algorithm using SJF. The arrival time and first CPU bursts of different jobs should be input to the system. The output should give the Gantt chart and waiting time for each process and average times.

Write the simulation program for preemptive scheduling algorithm using SJF. The arrival time and first CPU bursts of different jobs should be input to the system. The output should give the Gantt chart and waiting time for each process and average times.

Program:

#include <stdio.h>
#include <stdlib.h>

struct sch{
 int wt,at,ft,bt,st;
}pr[50],temp[50];
int rq[50],x,n,timer;
void addp(){
 int i;
 for(i=0;i<n;i++){
  if(pr[i].at==timer){
   rq[++x]=i;
  }
 }
}

int selectp(){
 int pp,i;
 if(x<0){
  return(-1);
 }else{
  pp=rq[0];
  for(i=1;i<=x;i++){
   if(temp[pp].bt>temp[i].bt){
    pp=i;
   }
  }
  for(i=pp;i<x;i++){
   rq[i]=rq[i+1];
  }
  x--;
  return(pp);
 }
}

void main(){
 setbuf(stdout,NULL);
 int i,t,p;
 float awt;
 timer=0;
 x=-1;
 printf("Enter the Number of processes:");
 scanf("%d",&n);
 for(i=0;i<n;i++){
  printf("\nEnter arrival time:");
  scanf("%d",&pr[i].at);
  printf("\nEnter bursts time:");
  scanf("%d",&pr[i].bt);
  temp[i]=pr[i];
 }
 t=0;
 addp();
 while(t<n){
  p=selectp();
  if(p==-1){
   printf("idle|");
   timer++;
   addp();
  }else{
   if(pr[p].bt==temp[p].bt){
    pr[p].st=timer;
   }
   printf("P%d|",p);
   temp[p].bt--;
   timer++;
   addp();
   if(temp[p].bt<=0){
    pr[p].ft=timer;
    t++;
   }else{
    rq[++x]=p;
   }
  }
 }
 awt=0;
 printf("\nWaiting time of each Process:");
 for(i=0;i<n;i++){
  pr[i].wt=(pr[i].ft-pr[i].at)-pr[i].bt;
  printf("\nP%d=%d",i,pr[i].wt);
  awt+=pr[i].wt;
 }
 awt = awt/n;
 printf("\nAverage Waiting time:%f",awt);
}