Newton Forward and Backward Method

/* Interpolation by Newton Forward and Backward formulae */
#include<stdio.h>
#include<conio.h>

void main()
{
int n,i,j,op;
float x[10],y[10],xx,yy,d[3][10],u,t;
clrscr();
printf("\nNo. of pairs of points");
scanf("%d",&n);
for(i=0;i<n;i++)
{
 printf("%d th value of x and  wanted\t",i+1);
 scanf("%f%f",&x[i],&y[i]);
}
 for(i=0;i<3 && i<n-1;i++)
 for(j=0;j<n-i-1;j++)
 if(i==0)
  d[i][j]=y[j+1]-y[j];
  else
  d[i][j]=d[i-1][j+1]- d[i-1][j];
  while(1)
  {
  printf(" Give option: Press 1 for Forward: 2 for Backward:3 for Exit\n ");
  scanf("%d",&op);
  if(op==3)  break;
  printf("Give value of x for which y to be interpolated");
  scanf("%f",&xx);
  switch(op)
  {
   case 1: u=(xx-x[0])/(x[0]);yy=y[0];t=1;
       for(i=0;i<3 && i<n-1;i++)
       {
t*=(u-i)/(i+1);
yy+=t*d[i][0];
       }
  break;
   case 2: u=(xx-x[n-1])/(x[i]-x[0]);yy=y[n-1];t=1;
  for(i=0;i<3&&i<n-1;i++)
       {
t*=(u+i)/(i+1);
yy+=t*d[i][n-i-2];
       }
   }
   printf("x=%f\t y=%f\n",xx,yy);
   getch();
   }
  }