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Saturday, 1 June 2013

C code for Shortest Job First Scheduling

Shortest job first scheduling(SJF Scheduling):
In this scheduling CPU is always assigned to the process with least CPU burst requirement. If the two processes having the same length, next CPU burst, FCFS scheduling is used i.e. one which arrives first, will be taken up first by the CPU. This algorithm can be preemptive or non-preemptive.  

/* C program to implement Shortest Job First (SJF) Algorithm */

#include<stdio.h>
#include<conio.h>
int initialize();
int p[10],a[10],b[10],w[10],ta[10],t1,gantt[20][2];
void main()
 {
  int i,j,n,k,t,e=0,m=0;
  float aw,at,sum1;
  clrscr();
  printf("\n\nP  A  B  W  TAT\n\n");
  n=initialize();
   for(i=0;i<n;i++)
    {
     for(j=i+1;j<n;j++)
      {
       if((a[i]>a[j]) || ((a[i]==a[j]) && (b[i]>b[j])))
    {
     t=a[i];
     a[i]=a[j];
     a[j]=t;

     t=b[i];
     b[i]=b[j];
     b[j]=t;

     t=p[i];
     p[i]=p[j];
     p[j]=t;
    }
      }
    }
    k=a[0]+b[0];
for(i=1;i<n;i++)
    {
     for(j=i+1;j<n;j++)
      {
       if(b[i]>b[j] && k>=a[j])
    {
     m=1;

     t=b[i];
     b[i]=b[j];
     b[j]=t;

     t=a[i];
     a[i]=a[j];
     a[j]=t;

     t=p[i];
     p[i]=p[j];
     p[j]=t;
    }
      }
      if (m==0)
       k=k+b[i];
      else
       k++;
      m=0;
   }

t1=0;
 for(i=0;i<n;i++)
  {
  if (t1-a[i]<0)
    {
     gantt[e][0]=-1;
     gantt[e++][1]=t1;
     t1+=a[i]-t1;
    }
   if(i==0)
    w[i]=0;
   else
    w[i]=t1-a[i];
   gantt[e][0]=a[i];
   gantt[e++][1]=t1;
   t1+=b[i];
  }
  gantt[e][1]=t1;
 for(i=0;i<n;i++)
  {
   ta[i]=b[i]+w[i];
  }
 for(i=0;i<n;i++)
 {
    printf("%d  %d  %d  %d  %d\n",p[i],a[i],b[i],w[i],ta[i]);
 }
printf("\nAverage waiting time is:");
 sum1=0.0;
  for(i=0;i<n;i++)
   {
    sum1+=w[i];
   }
 aw=sum1/n;
 printf("%.2f",aw);

 printf("\nAverage turn around time is:");
 sum1=0.0;
  for(i=0;i<n;i++)
   {
    sum1+=ta[i];
   }
 at=sum1/n;
 printf("%.2f",at);
printf("\n\nThe Gantt chart is:\n\n");
 /*for(i=0;i<n;i++)
  {
   printf("|%d",p[i]);
    if(i==n-1)
     printf("|");
  } */
  printf (" ");
  for (i=0;i<e;i++)
   printf ("--- ");
  printf ("\n");
  for (i=0;i<e;i++)
   printf (gantt[i][0]==-1?"|   ":"| %d ",gantt[i][0]);
  printf ("|\n ");
  for (i=0;i<e;i++)
   printf ("--- ");
   printf ("\n");
  for (i=0;i<=e;i++)
   printf ("%d   ",gantt[i][1]);
 getch();
}

int initialize()
{
  int n,n1,n2,n3,i=0;
  FILE *fp;
  fp=fopen("sjf.txt","r");
  while(fscanf(fp,"%d%d%d",&n1,&n2,&n3)!=EOF)
    {
        p[i]=n1;
        a[i]=n2;
        b[i]=n3;
          i++;
    }
  return i;
}



Input File:

1 0 3
2 1 3
3 2 2

//Output Of the above program:-

C code for Shortest Job First Scheduling


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