NEWTON DIVIDED DIFFERENCE FORMULA

#include<stdio.h>

#include<conio.h>

#include<stdlib.h>

#include<math.h>

#define n 5

int main()

{

    float y[n],x[n],d[n-1],xa,u,sum=0,tnum,tden;

    int i,j,l,k,m;

   // clrscr();

    printf("enter the values of interpolation x points\n");

    for(i=1;i<=n;i++)

    scanf("%f",&x[i]);

    printf("enter the corresponding values of y\n");

    for(i=1;i<=n;i++)

    scanf("%f",&y[i]);

    printf("enter the value of x at which y(x) is needed\n");

    scanf("%f",&xa);

    if(fabs(xa-x[1])>fabs(xa-x[n]))

    {

       printf("this is not a suitable formula\n");

         return(1);

     }

     m=n-1;

     for(i=1;i<n;i++)

                d[i]=y[i+1]-y[i];

                 for(i=2;i<n;i++)

                 {

                  for(l=i;i>l;l--)

                  printf("\t");

                   for(j=i;j<n;j++)

                   {

                   k=m-j+i;

                   d[k]=d[k]-d[k-1];

                   }

                   }

                   u=((xa-x[1])/fabs(x[2]-x[1]));

                   sum=y[1];

                   tnum=u;

                   tden=1.0;

                   for(i=1;i<n;i++)

                   {

                   sum=sum+(tnum/tden)*d[i];

                   tnum=tnum*(u-1);

                   tden=tden*(i+1);

                   }

                   printf("the value of y is %f\n",sum);

                   getch();

 }