8.Write program to implement SJF scheduling algorithm (Preemptive)

Write program to implement SJF scheduling algorithm (Preemptive)

//cskecode

//cskecode.blogspot.com
#include<iostream>
using namespace std;
class sched{
public:
int n,bt[10],at[10],tat[10],wt[10],rt[10],finish[10],twt,ttat,total;
void readData();
void computeSRT();
void Init();
void dispTime();
int getNextProcess(int);
};

void sched::readData()
{
cout<<"Enter no. of processes\n";
cin>>n;
cout<<"Enter the burst times in order :\n";
for(int i=0;i<n;i++)
cin>>bt[i];
cout<<"Enter the arrival times in order:\n";
for(int i=0;i<n;i++)
cin>>at[i];
}

void sched::Init()
{
total=0;
twt=0;
ttat=0;
for(int i=0; i<n; i++)
{
 rt[i]=bt[i];
finish[i]=0;
wt[i]=0;
tat[i]=0;
total+=bt[i];
}
}

void sched::computeSRT()
{
 readData();
Init();
int time,next=0,old,i;
cout<<"Gantt Chart\n ";
for(time=0;time<total;time++)
{
old=next;
next=getNextProcess(time);
if(old!=next || time==0) 
{
cout<<"("<<time<<")|==P"<<next+1<<"==|";
}
rt[next]=rt[next]-1;
if(rt[next]==0) 
{
finish[next]=1;
}
for(i=0;i<n;i++)
if(i!=next && finish[i]==0 && at[i]<=time)
wt[i]++;
}
cout<<"("<<total<<")"<<endl;
for(i=0;i<n;i++)
if(!finish[i]) {cout<<"Scheduling failed, cannot continue\n"; return;}
dispTime();
}

int sched::getNextProcess(int time)
{ 
int i,low;
for(i=0;i<n;i++)
if(finish[i]==0){low=i; break; }
for(i=0;i<n;i++)
if(finish[i]!=1)
if(rt[i]<rt[low] && at[i]<=time)
low=i;
return low;
}

void sched::dispTime()
{
for(int i=0;i<n;i++)
{
twt+=wt[i];
tat[i]=wt[i]+bt[i];
ttat+=tat[i];
cout<<"Waiting time for P"<<(i+1)<<" = "<<wt[i]<<", Turnaround time = "<<tat[i]<<endl;
}
cout<<"Avg Waiting time = "<<(double)twt/n<<" and Avg Turnaround time = "<<(double)ttat/n<<endl;
cout<<"Scheduling complete\n";
}

int main()
{
sched s;
s.computeSRT();
}
//cskecode.blogspot.com


Output: