Notes

1. TO SHOW THE IMPLEMENTATION OF FORK ( ) ALGORITHM
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

int main () {
pid_t pid;
int status;
pid = fork(); // Create a child process
if (pid < 0) { // Error occurred
fprintf(stderr, "Fork failedn");
exit(1);
} else if (pid == 0) { // Child process
printf("Child process - pid: %dn", getpid());
exit(0);
} else { // Parent process
printf("Parent process - pid: %dn", getpid());
wait(&status); // Wait for child to terminate
printf("Child exited with status %dn", status);
}
return 0;
}

2. A program to implement First Come First Served (FCFS) algorithm.

#include<stdio.h>
int main()
{
int n,bt[20],wt[20],tat[20],avwt=0,avtat=0,i,j;
printf("Enter total number of processes(maximum 20):");
scanf("%d",&n);
printf("nEnter Process Burst Timen");
for(i=0;i<n;i++)
{
printf("P[%d]:",i+1);
scanf("%d",&bt[i]);
}
wt[0]=0;
for(i=1;i<n;i++)
{
wt[i]=0;
for(j=0;j<i;j++)
wt[i]+=bt[j];
}
printf("nProcessttBurst Timet Waiting Timet Turnaround Time");
for(i=0;i<n;i++)
{
tat[i]=bt[i]+wt[i];
avwt+=wt[i];
avtat+=tat[i];
printf("nP[%d]tt%dtt%dtt%d",i+1,bt[i],wt[i],tat[i]);
}
avwt/=i;
avtat/=i;
printf("nnAverage Waiting Time:%d",avwt);
printf("nAverage Turnaround Time:%d",avtat);
return 0;
}

3. A program to implement Shortest Job First (SJF) algorithm.

#include<stdio.h>
#include<conio.h>
int main()
{
int n, BT[10], WT, TAT=0, i, j, temp;
float AWT, TWT=0, ATAT, TTAT=0;
printf("Enter total number of process:t");
scanf("%d",&n);
for(i=0;i<n;i++)
{
printf("Enter Burst time of process %d:t",i+1);
scanf("%d",&BT[i]);
}
for(i=0;i<n;i++)
{
for(j=i+1;j<n;j++)
{
if(BT[i]>BT[j])
{
temp=BT[i];
BT[i]=BT[j];
BT[j]=temp;}
}
}
printf("nProcessttBTttWTttTAT");
for(i=0;i<n;i++)
{
TAT=BT[i]+WT;
printf("n%dtt%dtt%dtt%d",i+1,BT[i],WT,TAT);
TWT=TWT+WT;
TTAT=TTAT+TAT;
WT=WT+BT[i];
}
AWT=TWT/n;
ATAT=TTAT/n;
printf("nAverage waiting time:%f",AWT);
printf("nAverage Turn around time:%f",ATAT);
return 0;
}

4. Write a program to show the implementation of Round Robin (RR) algorithm.

#include<stdio.h>
#include<conio.h>
int main()
{
int count, n, time, remain, flag=0, time_quantum;
int wait_time=0, turnaround_time=0, at[10], bt[10], rt[10];
printf("Enter total process:t");
scanf("%d",&n);
remain=n;
for(count=0;count<n;count++)
{
printf("Enter Arrival time for process %d:t",count+1);
scanf("%d",&at[count]);
printf("Enter Burst time for process %d:tt",count+1);
scanf("%d",&bt[count]);
rt[count]=bt[count];
}
printf("Enter quantum time:t");
scanf("%d",&time_quantum);
printf("nProcessttTurn Around TimettWaiting Timen");
for(time=0,count=0;remain!=0;)
{
if(rt[count]<=time_quantum&&rt[count]>0)
{
time+=rt[count];
rt[count]=0;
flag=1;
}
else if(rt[count]>0)
{
rt[count]-=time_quantum;
time+=time_quantum;
}
if(rt[count]==0&&flag==1)
{
remain--;
printf("P[%d]tt%dtttt%dn",count+1, time-at[
count], time- at[count]-bt[count]);
wait_time+=time-at[count]-bt[count];
turnaround_time+=time-at[count];
flag=0;
}
if(count==n-1)
count=0;
else if(at[count+1]<=time)
count++;
else count=0;
}
printf("nAverage waiting time=%fn",wait_time*1.0/n);
printf("Average turnaround time=%f",turnaround_time*1.0/n);
return 0;
}

5. WAP to find the page fault that can occur in a given reference string using FIFO page replacement algorithm.

#include<stdio.h>
#include<stdlib.h>
int n,ref[100],fs,frame[100],count=0;
int f=-1, r=-1;
void input();
void show();
void cal();
void queue(int k);
int main()
{
printf("*********FIFO Page Replacement Algorithm*********n");
input();
cal();
show();
return 0;
}void input()
{
int i;
printf("Enter the no. of pages in Reference string:-t");
scanf("%d",&n);
printf("Enter Reference string:-n");
for(i=0;i<n;i++)
{
scanf("%d",&ref[i]);
}
printf("Enter the frame size:-t");
scanf("%d",&fs);
}
void cal()
{
int i;
for(i=0;i<fs;i++)
{
frame[i]=-1;
}
for(i=0;i<n;i++)
{
queue(ref[i]);
}
}

void queue(int k)
{
int i;
for(i=0;i<fs;i++)
{
if(frame[i]==k)
{
return;
}
}
if(r==fs-1)
{
r=0;
}
else if(r==-1)
{
f=0;
r=0;
}
else
{
r=r+1;
}
frame[r]=k;
count++;
}
void show()
{
printf("Page faults=%d",count);
}


6. WAP to find the page fault that can occur in a given reference string using LRU page replacement algorithm.
#include<stdio.h>
#include<conio.h>
int n, ref[100], fs, frame[100], count=0;
void input();
void show();
void cal();
int main()
{
printf("*****************LRU Page Replacement Algorithm*******************n");
input();
cal();
show();
getch();
return 0;
}
void input()
{
int i;
printf("Enter no. of pages in reference string:-t");
scanf("%d",&n);
printf("Enter the reference string:-n");
for(i=0;i<n;i++)
scanf("%d",&ref[i]);
printf("Enter the frame size:-t");
scanf("%d",&fs);
}
void cal()
{
int i, j, k=0, c1, c2[100], r, temp[100], t;
frame[k]=ref[k];
count++;
k++;
for(i=1;i<n;i++)
{
c1=0;
for(j=0;j<fs;j++)
{
if(ref[i]!=frame[j])
c1++;
}
if(c1==fs)
{
count++;
if(k<fs)
{
frame[k]=ref[i];
k++;
}
else
{
for(r=0;r<fs;r++)
{
c2[r]=0;
for(j=i-1;j<n;j--)
{
if(frame[r]!=ref[j])
c2[r]++;
else
break;
}
}
for(r=0;r<fs;r++)
temp[r]=c2[r];
for(r=0;r<fs;r++)
{
for(j=r;j<fs;j++)
{
if(temp[r]<temp[j])
{
t=temp[r];
temp[r]=temp[j];
temp[j]=t;
}
}
}
for(r=0;r<fs;r++)
{
if(c2[r]==temp[0])
frame[r]=ref[i];
}
}
}
}
}

void show()
{
printf("Page faults = %d",count);
}


7. WAP to find the page fault that can occur in a given reference string using Optimal page replacement algorithm.

#include<stdio.h>
#include<conio.h>
int n;
int findmax(int a[])
{
int max, i, k=0;
max=a[0];
for(i=0;i<n;i++)
{
if(max<a[i])
{
max=a[i];
k=i;
}
}
return k;
}
int main()
{
int seq[30], fr[5], pos[5], find, flag, max, i, j, m, k, t, s;
int count=1, pf=0, p=1;
printf("Length of reference string:-t");
scanf("%d",&max);
printf("nThe reference string:-n");
for(i=0;i<max;i++)
scanf("%d",&seq[i]);
printf("nNumber of frames:-t");
scanf("%d",&n);

fr[0]=seq[0];
pf++;
printf("%dt",fr[0]);
i=1;

while(count<n)
{
flag=1;
p++;
for(j=0;j<i;j++)
{
if(seq[i]==seq[j])
flag=0;
}
if(flag!=0)
{
fr[count]=seq[i];
printf("%dt",fr[count]);
count++;
pf++;
}
i++;
}
printf("n");
for(i=p;i<max;i++)
{
flag=1;
for(j=0;j<n;j++)
{
if(seq[i]==fr[j])
flag=0;
}
if(flag!=0)
{
for(j=0;j<n;j++)
{
m=fr[j];
for(k=i;k<max;k++)
{
if(seq[k]==m)
{
pos[j]=k;
break;
}
else
pos[j]=1;
}
}
for(k=0;k<n;k++)
{
if(pos[k]==1)
flag=0;
}
if(flag!=0)
s=findmax(pos);
if(flag==0)
{
for(k=0;k<n;k++)
{
if(pos[k]==1)
{
s=k;
break;
}
}
}
fr[s]=seq[i];
for(k=0;k<n;k++)
printf("%dt",fr[k]);
pf++;
printf("n");
}
}
printf("nThe no. of page faults are %d",pf);
getch();
return 0;
}