sjfn.cpp

// C++ program to implement Shortest Job first
#include<bits/stdc++.h>
using namespace std;

struct Process
{
   int pid; // Process ID
   int bt;  // Burst Time
};

// This function is used for sorting all
// processes in increasing order of burst
// time
bool comparison(Process a, Process b)
{
     return (a.bt < b.bt);
}

// Function to find the waiting time for all
// processes
void findWaitingTime(Process proc[], int n, int wt[])
{
    // waiting time for first process is 0
    wt[0] = 0;

    // calculating waiting time
    for (int i = 1; i < n ; i++ )
        wt[i] = proc[i-1].bt + wt[i-1] ;
}

// Function to calculate turn around time
void findTurnAroundTime(Process proc[], int n,
                        int wt[], int tat[])
{
    // calculating turnaround time by adding
    // bt[i] + wt[i]
    for (int i = 0; i < n ; i++)
        tat[i] = proc[i].bt + wt[i];
}

//Function to calculate average time
void findavgTime(Process proc[], int n)
{
    int wt[n], tat[n], total_wt = 0, total_tat = 0;

    // Function to find waiting time of all processes
    findWaitingTime(proc, n, wt);

    // Function to find turn around time for all processes
    findTurnAroundTime(proc, n, wt, tat);

    // Display processes along with all details
    cout << "\nProcesses "<< " Burst time "
         << " Waiting time " << " Turn around time\n";

    // Calculate total waiting time and total turn
    // around time
    for (int i = 0; i < n; i++)
    {
        total_wt = total_wt + wt[i];
        total_tat = total_tat + tat[i];
        cout << " " << proc[i].pid << "\t\t"
             << proc[i].bt << "\t " << wt[i]
             << "\t\t " << tat[i] <<endl;
    }

    cout << "Average waiting time = "
         << (float)total_wt / (float)n;
    cout << "\nAverage turn around time = "
         << (float)total_tat / (float)n;
}

// Driver code
int main()
{
    Process proc[] = {{1, 6}, {2, 8}, {3, 7}, {4, 3}};
    int n = sizeof proc / sizeof proc[0];

    // Sorting processes by burst time.
    sort(proc, proc + n, comparison);

    cout << "Order in which process gets executed\n";
    for (int i = 0 ; i < n; i++)
        cout << proc[i].pid <<" ";

    findavgTime(proc, n);
    return 0;
}