Regula Falsi. C

 //for implementation of regula falsi Method for
// solving equations
#include<stdio.h>
#include<math.h>
#define MAX_ITER 1000000
#define err 0.00001

double f(double x)
{
//    return x*x - 4*x - 10;
return x*x*x - 4*x - 9;
}
// Prints root of f(x) in interval [a, b]

void regulaFalsi(double a, double b)
{
int count=0;
printf("finding the appreox root of the eqn. by REGULA FALSI    method");
    if (f(a) * f(b) >= 0)
    {
        printf("You have not assumed right a and b\n");
        return;
    }
    double c = a;  // Initialize result
    printf("\na\t\tb\t\tf(a)\t\tf(b)\t\tc\t\tf(c)\n");

    for (int i=0; i < MAX_ITER; i++)
    {
        printf("%.4f \t\t%.4f \t\t%.4f\t\t%.4f",a,b,f(a),f(b));
        // Find the point that touches x axis
        c = (a*f(b) - b*f(a))/ (f(b) - f(a));
        printf("\t\t%.4f\t\t%.4f\n",c,f(c));
        // Check if the above found point is root
       if (f(c)<=0.00001 && f(c)>=-0.00001)
       {    // if(fabs(a-c)>err)
        break;
        }
        // Decide the side to repeat the steps
     else   if (f(c)*f(a) < 0)
            b = c;
        else if(f(c)*f(a) > 0)
            a = c;

            count++;
    }
    printf( "The value of root is :%.4f ", c);
    printf(" the no of iterations required is %d",count);
}

void GetRootRange(double *L, double *U)
 {
 double y;
 for(y=-999999.0l;y<999999.0l;y=y+0.1)
 {
 if(f(y)*f(y+0.1)<0.0)
 {fflush(stdin);
 *L=y;*U=y+0.1;
 return;
 }
 }
 }
// Driver program to test above ftion :""

int main()
{
    // Initial values assumed
    double a , b  ;
    GetRootRange(&a,&b);
    regulaFalsi(a, b);
    return 0;
}