lagrange.c

#include <stdio.h>
#include <math.h>

float lagrange(float x, int n, float xi[], float yi[])
{
  float sum = 0;
  for (int i = 0; i < n; i++)
  {
    float product = 1;
    for (int j = 0; j < n; j++)
    {
      if (i != j)
      {
        product *= (x - xi[j]) / (xi[i] - xi[j]);
      }
    }
    sum += product * yi[i];
  }
  return sum;
}

int main()
{
  float x;
  int n;
  float xi[10], yi[10];

  printf("Enter the value of n: ");
  scanf("%d", &n);

  for (int i = 0; i < n; i++)
  {
    printf("Enter the value of x(%d): ", i + 1);
    scanf("%f", &xi[i]);
    printf("Enter the value of y(%d): ", i + 1);
    scanf("%f", &yi[i]);
  }

  printf("Enter the value of x: ");
  scanf("%f", &x);

  printf("The value of f(x) is %.4f\n", lagrange(x, n, xi, yi));
  return 0;
}