program_1.c

// Program to demo LRU page replacement algorithm

#include <stdio.h> 

int main()
{
   int i,j,k,min,rs[25],m[10],count[10],flag[25],n,f,pf=0,next=1;

   printf("Enter length of the reference string: ");
   scanf("%d", &n);

   printf("Enter the reference string: "); 
   for(i=0; i<n; i++)
   {
      scanf("%d", &rs[i]);
      flag[i] = 0; 
   }

   printf("Enter the number of frames: "); 
   scanf("%d", &f); 
  
   for(i=0; i<f; i++)
   {
      count[i] = 0; 
      m[i] = -1;
   }

   printf("\nLRU PageReplacement process--\n"); 
   for(i=0;i<n;i++)
   {
      for(j=0;j<f;j++)
      {
         if(m[j] == rs[i])
         {
            flag[i] = 1; 
            count[j] = next; 
            next++;
         }
      }

      if(flag[i] == 0)
      {
         if(i<f)
         {
            m[i] = rs[i];
            count[i] = next; 
            next++;
         }
         else
         {
            min = 0; 

            for(j=1;j<f;j++)
              if(count[min]>count[j])
                 min=j; 
            m[min] = rs[i];
            count[min] = next; 
            next++;
         }

         pf++;
      }

      for(j=0;j<f;j++) 
         printf("%d\t", m[j]); 

      if(flag[i] == 0)
         printf("PF No. -- %d" , pf);

      printf("\n");
   }
 
   printf("\nThe number of page faults using LRU are %d\n",pf); 
   
   return 0;
}