newton backward interpolation

#include<stdio.h>
void main()
{
    double ax[50],ay[50],diff[50][50];
    double x,h,yp,nr=1,p,dr=1;
    int n,i,j;
    printf("enter the nuber of known data values:");
    scanf("%d",&n);
    printf("enter the values of x and y respectively\n");
    for(i=0;i<n;i++)
    {
        printf("x%d=",i);
        scanf("%lf",&ax[i]);
        printf("  y%d=",i);
        scanf("%lf",&ay[i]);
        printf("\n");
    }
    printf("enter the value of x to find y\n");
    scanf("%lf",&x);
    h=ax[1]-ax[0];
    for(i=0;i<n;i++)
        diff[i][0]=ay[i+1]-ay[i];
    for(j=1;j<(n-1);j++)
    {
        for(i=0;i<=(n-j);i++)
            diff[i][j]=diff[i+1][j-1]-diff[i][j-1];
    }
    yp=ay[n-1];
    i=n-1;
    p=(x-ax[n-1])/h;
    for(j=1;j<(n-1);j++)
    {
        nr=nr*(p+j-1);
        dr=dr*j;
        yp=yp+(nr/dr)*diff[i-1][j-1];
        i--;
    }
    printf("For x = %.4lf y = %.4lf\n",x,yp);
}

OUTPUT:
enter the nuber of known data values:5
enter the values of x and y respectively
x0=200
  y0=15.04

x1=250
  y1=16.81

x2=300
  y2=18.42

x3=350
  y3=19.9

x4=400
  y4=21.27

enter the value of x to find y
218
For x = 218.0000 y = 15.7021
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