Program to implement the Newton- Gregory forward interpolation.

#include<stdio.h>
#include<conio.h>
#define MaxN 100
#define Order_of_diff 4

void main ()
{
float arr_x[MaxN+1], arr_y[MaxN+1], numerator=1.0, denominator=1.0, x, y, p, h, diff_table[MaxN+1][Order_of_diff+1];
int i,j,n,k;
clrscr();

printf("Enter the value of n \n");
scanf("%d",&n);
printf("Enter the values of x and y");

for(i=0; i<=n; i++)
scanf("%f%f", &arr_x[i], &arr_y[i]);
printf("Enter the value of x at which value of y is to be calculated");
scanf("%f", &x);
h=arr_x[1]-arr_x[0];

for(i=0; i<=n-1; i++)
diff_table[i][1]=arr_y[i+1]-arr_y[i];/*Creating the difference table and calculating first order differences*/
for(j=2; j<=Order_of_diff; j++)/*Calculating higher order differences*/
for(i=0; i<=n-j; i++)
diff_table[i][j]=diff_table[i+1][j-1] - diff_table[i][j-1];
i=0;

while(!(arr_x[i]>x)) /* Finding x0 */
i++;
i--;
p=(x-arr_x[i])/h;
y=arr_y[i];

for (k=1; k<=Order_of_diff; k++)
{
numerator *=p-k+1;
denominator *=k;
y +=(numerator/denominator)*diff_table[i][k];
}
printf("When x=%6.1f, y=%6.2f\n",x, y);
getch();
}
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