Implement Method of Bisection using C

/* Method of Bisection

 Equation: x^3-4x-9=0*/
#include<stdio.h>
#include<math.h>
void main()
{
 float a,b,k,m;
 float f(float);
 printf("\nEnter first initial value:: ");
 scanf("%f",&a);
 printf("\nEnter second initial value:: ");
 scanf("%f",&b);
 while(fabs(a-b)>0.00001)
 {
  m=(a+b)/2;
  k=f(m);
  if(k>0)
 b=m;
  else
 a=m;
 }
 printf("\nRoot is:: %f",m);
}
float f(float x)
{
 return (x*x*x)-(4*x)-9;
}