# C Program for Lagrange Interpolation Method (with Output)

#### This program implements Lagrange Interpolation Formula in C Programming Language.

In this C program, x and y are two array for storing x data and y data respectively. xp is interpolation point given by user and output of Lagrange interpolation method is obtained in yp.

## C Source Code: Lagrange Interpolation

``````
#include<stdio.h>
#include<conio.h>

void main()
{
float x[100], y[100], xp, yp=0, p;
int i,j,n;
clrscr();
/* Input Section */
printf("Enter number of data: ");
scanf("%d", &n);
printf("Enter data:\n");
for(i=1;i<=n;i++)
{
printf("x[%d] = ", i);
scanf("%f", &x[i]);
printf("y[%d] = ", i);
scanf("%f", &y[i]);
}
printf("Enter interpolation point: ");
scanf("%f", &xp);
/* Implementing Lagrange Interpolation */
for(i=1;i<=n;i++)
{
p=1;
for(j=1;j<=n;j++)
{
if(i!=j)
{
p = p* (xp - x[j])/(x[i] - x[j]);
}
}
yp = yp + p * y[i];
}
printf("Interpolated value at %.3f is %.3f.", xp, yp);
getch();
}
``````

## C Program Output: Lagrange Interpolation

```Enter number of data: 5 ↲
Enter data:
x[1] = 5 ↲
y[1] = 150 ↲
x[2] = 7 ↲
y[2] = 392 ↲
x[3] = 11 ↲
y[3] = 1452 ↲
x[4] = 13 ↲
y[4] = 2366 ↲
x[5] = 17 ↲
y[5] = 5202 ↲
Enter interpolation point: 9 ↲
Interpolated value at 9.000 is 810.000.

Note: ↲ indicates ENTER is pressed.
```