# Lagrange Interpolation Method Using C++ 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<iostream>
#include<conio.h>

using namespace std;

int main()
{
float x[100], y[100], xp, yp=0, p;
int i,j,n;

/* Input Section */
cout<<"Enter number of data: ";
cin>>n;
cout<<"Enter data:"<< endl;
for(i=1;i<=n;i++)
{
cout<<"x["<< i<<"] = ";
cin>>x[i];
cout<<"y["<< i<<"] = ";
cin>>y[i];
}
cout<<"Enter interpolation point: ";
cin>>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];
}
cout<< endl<<"Interpolated value at "<< xp<< " is "<< yp;

return 0;
}

``````

## C++ 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 is 810
```