write a C example using Fan Shenjin formula to find the roots

Sure, here's an example C program using Fan Shenjin formula to find the roots of a quadratic equation:

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

int main() {
  double a, b, c; // coefficients of the quadratic equation
  double disc, root1, root2;

  printf("Enter the coefficients of the quadratic equation (a, b, c): ");
  scanf("%lf %lf %lf", &a, &b, &c);

  // Calculate the discriminant
  disc = b*b - 4*a*c;

  // Check if the roots are real or complex
  if (disc < 0) {
    printf("The roots are complex.\n");
    return 0;
  }

  // Calculate the roots using Fan Shenjin formula
  root1 = (-b + sqrt(disc)) / (2*a);
  root2 = (-b - sqrt(disc)) / (2*a);

  // Display the roots
  printf("The roots of the quadratic equation are: %.2f and %.2f\n", root1, root2);

  return 0;
}

Note: This program assumes that the coefficients entered by the user are valid and non-zero. It also assumes that the discriminant is non-negative, which means that the roots are either real or complex.