rrs.c

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

struct rrs {
  int pid, atime, btime, tempb, ctime, tatime, wtime;
  short isTraversed;
};

void main () {
  
  int i, j, k, n, count = 0, qt, curr_time = 0, leucpid; 
  float ttatime = 0, twtime = 0;

  printf ("\nRRS CPU SCHEDULING\n\nEnter the no. of processes -> ");
  scanf ("%d", &n);
  
  struct rrs p[n];
  // dynamic allocation for ready queue
  int *q;
  q = (int *)malloc (sizeof (int));

  printf ("\nEnter the values -> \n");
  printf ("P[pid]\tAT\tBT\n");
  for (i = 0; i < n; i++) {

    p[i].isTraversed = 0;
    p[i].pid = i;
    printf ("P[%d]\t", p[i].pid);
    scanf ("%d %d", &p[i].atime, &p[i].btime); 
    p[i].tempb = p[i].btime; // burstTime left after preemption stored in p[i].tempb
    
  }
  
  printf ("\nEnter the time quantum -> ");
  scanf ("%d", &qt);

  j = 0; // ready queue index
  k = 0; // completed process index in ready queue 

  leucpid = -1; // stores id of last executed uncomplete process
  
  printf ("\nP\tAT\tBT\tCT\tTAT\tWT");
  while (count != n) { 
    
    for (i = 0; i < n; i++) 
      if (p[i].isTraversed == 0) // checks whether a process is traversed once to avoid repetition of processes in the ready queue
        if (curr_time >= p[i].atime) { 
          q[j] = i;
          p[q[j]].isTraversed = 1;
          j++;
        }

    if (leucpid != -1) { // for storing id of the preempted process
      q[j] = leucpid;
      j++;
    }

    if (p[q[k]].tempb <= qt) {

      curr_time += p[q[k]].tempb;
      p[q[k]].tempb = 0;

      p[q[k]].ctime = curr_time;
      p[q[k]].tatime = p[q[k]].ctime - p[q[k]].atime;
      p[q[k]].wtime = p[q[k]].tatime - p[q[k]].btime;
      ttatime += p[q[k]].tatime;
      twtime += p[q[k]].wtime;

      printf ("\nP%d\t%d\t%d\t%d\t%d\t%d", p[q[k]].pid, p[q[k]].atime, p[q[k]].btime, p[q[k]].ctime, p[q[k]].tatime, p[q[k]].wtime);

      leucpid = -1;
      k++;
      count++;
    }
    else if (p[q[k]].tempb > qt) {

      curr_time += qt;
      p[q[k]].tempb -= qt;

      leucpid = p[q[k]].pid;

      k++;

    }

  }

  printf ("\n\nAverage Turnaround Time: %f", ttatime/n);
  printf ("\nAverage Waiting Time: %f\n\n", twtime/n);

}