Roots of equation

#include <stdio.h>
#include <math.h> 
double f(double x) {
    return exp(x) - x -2;   
}    
double root(double a, double b, double (*fun)(double));

int main(void)
{
    printf("Roots of equation are : %.12f  %.12f\n", root(1,2, f), root(-2,0,f));
    return 0;
}

double root(double a, double b, double (*fun)(double)) {
    double c;
   const double z = 1e-10;
   while ( b - a > z)
   {
       c = (a + b) / 2;
        if (fun(a) * fun(c) < 0) {
            b = c;
       } else  {
           a = c;
       }    
    }
    return c;
}