First in First out page replacement algorithm

page replacement algorithm:-
In a  computer operating system that uses paging for virtual memory management, page replacement algorithms decide which memory pages to page out (swap out, write to disk) when a page of memory needs to be allocated. Paging happens when a page fault occurs and a free page cannot be used to satisfy the allocation, either because there are none, or because the number of free pages is lower than some threshold.
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PROGRAM:-

#include<unistd.h>
#include<stdio.h>
int main()
 {
int tn;  // tn: total numbe rof pages
int fs;  // fs: frame size
int cnt; // to count no of page faults
int i,j,s,ss,pg;
int pr[20]; // page name
int fm[10]; //frame
printf("Enter number of pages    :   ");


scanf("%d",&tn);
printf("Enter size of frame  :   ");
scanf("%d",&fs);
printf("Enter page name :\n");
for(i=0;i<tn;i++)
{
printf("\t");
scanf("%d",&pr[i]);
 }
s=0;ss=0;
for(i=0;i<fs;i++)
{  
  fm[i]=-1;
 }
for(i=0;i<tn;i++)
 {
printf("\n page :   %d",pr[i]);
if(i<fs)
  {
pg=0;
for(j=0;j<fs;j++)
{
if(fm[j]==pr[i])  pg++;
}
if(pg==0)
{
fm[s]=pr[i]; s=(s+1)%fs; cnt++;
}
   }
else
   {   pg=0;
    for(j=0;j<fs;j++)
{
if(fm[j]==pr[i])  pg++;
}
if(pg==0)
   { fm[ss]=pr[i]; cnt++; ss=(ss+1)%fs; }
    }
printf("\n\t\t\t frame:");
for(j=0;j<fs;j++)
   {  if(fm[j]>-1)
printf("\t%d",fm[j]);
            }
}

printf("\n page fault :  %d\n",cnt);
 }

Output:-