Write the program to simulate Preemptive Shortest Job First (SJF) -scheduling

 Write the program to simulate Preemptive Shortest Job First (SJF) -scheduling. The
arrival time and first CPU-burst for different n number of processes should be input to
the algorithm. Assume the fixed IO waiting time (2 units). The next CPU-burst should be
generated randomly. The output should give Gantt chart, turnaround time and waiting
time for each process. Also find the average waiting time and turnaround time.
 
 #include<stdio.h>
#include<stdlib.h>
#include<string.h>
typedef struct process_info
{
 char pname[20];
 int at,bt,ct,bt1;
 struct process_info *next;
}NODE;
int n;
NODE *first,*last;
void accept_info()
{
 NODE *p;
 int i;
 printf("Enter no.of process:");
 scanf("%d",&n);
 for(i=0;i<n;i++)
 {
  p = (NODE*)malloc(sizeof(NODE));
  printf("Enter process name:");
  scanf("%s",p->pname);
  printf("Enter arrival time:");
  scanf("%d",&p->at);
  printf("Enter first CPU burst time:");
  scanf("%d",&p->bt);
  p->bt1 = p->bt;
  p->next = NULL;
  if(first==NULL)
   first=p;
  else
   last->next=p;
  last = p;
 }
}

void print_output()
{
 NODE *p;
 float avg_tat=0,avg_wt=0;
 printf("pname\tat\tbt\tct\ttat\twt\n");
 p = first;
 while(p!=NULL)
 {
  int tat = p->ct-p->at;
  int wt = tat-p->bt;
  avg_tat+=tat;
  avg_wt+=wt;
  printf("%s\t%d\t%d\t%d\t%d\t%d\n",
   p->pname,p->at,p->bt,p->ct,tat,wt);
  p=p->next;
 }
 printf("Avg TAT=%f\tAvg WT=%f\n",
   avg_tat/n,avg_wt/n);
}
void print_input()
{
 NODE *p;
 p = first;
 printf("pname\tat\tbt\n");
 while(p!=NULL)
 {
  printf("%s\t%d\t%d\n",
   p->pname,p->at,p->bt1);
  p = p->next;
 }
}


void sort()
{
 NODE *p,*q;
 int t;
 char name[20];
 p = first;
 while(p->next!=NULL)
 {
  q=p->next;
  while(q!=NULL)
  {
   if(p->at > q->at)
   {
    strcpy(name,p->pname);
    strcpy(p->pname,q->pname);
    strcpy(q->pname,name);
    t = p->at;
    p->at = q->at;
    q->at = t;
    t = p->bt;
    p->bt = q->bt;
    q->bt = t;
    t = p->ct;
    p->ct = q->ct;
    q->ct = t;
    t = p->bt1;
    p->bt1 = q->bt1;
    q->bt1 = t;
   }
   q=q->next;
  }
  p=p->next;
 }
}


int time;



NODE * get_sjf()

{
 NODE *p,*min_p=NULL;
 int min=9999;


 p = first;

 while(p!=NULL)
 {
  if(p->at<=time && p->bt1!=0 &&
   p->bt1<min)
  {
   min = p->bt1;
   min_p = p;
  }
  p=p->next;
 }
 return min_p;

}


struct gantt_chart

{
 int start;
 char pname[30];
 int end;
}s[100],s1[100];


int k;



void sjfp()

{
 int prev=0,n1=0;
 NODE *p;


 while(n1!=n)

 {
  p = get_sjf();


  if(p==NULL)

  {
   time++;
   s[k].start = prev;
   strcpy(s[k].pname,"*");
   s[k].end = time;
   prev = time;
   k++;
  }
  else
  {
   time++;
   s[k].start = prev;
   strcpy(s[k].pname, p->pname);
   s[k].end = time;
   prev = time;
   k++;
   p->ct = time;
   p->bt1--;
   if(p->bt1==0)
    n1++;
  }
  print_input(); 
  sort();
 }
}
void print_gantt_chart()
{
 int i,j,m;
 s1[0] = s[0];
 for(i=1,j=0;i<k;i++)
 {
  if(strcmp(s[i].pname,s1[j].pname)==0)
   s1[j].end = s[i].end;
  else
   s1[++j] = s[i];
 }
 printf("%d",s1[0].start);
 for(i=0;i<=j;i++)
 {
  m = (s1[i].end - s1[i].start);
  for(k=0;k<m/2;k++)
   printf("-");
  printf("%s",s1[i].pname);
  for(k=0;k<(m+1)/2;k++)
 printf("-");
  printf("%d",s1[i].end);
 }
}
int main()
{
 accept_info();
 sort();
 sjfp();
 print_output();
 print_gantt_chart();
 return 0;
}