#include <stdio.h>
 
double f (double x);
int sameSign(double x, double y);
double middleOf(double x, double y);
int isSmallNumber(double x);

/* K & R style, minor variant. More compact setup of else */
double findRootBetween(double a, double b)
{
    double l = a, u = b;
    while (!isSmallNumber(f(middleOf(l, u)))) { 
        if(sameSign(f(middleOf(l, u)), f(u))) {
            u = middleOf(l, u);
        } else {
            l = middleOf(l, u);
        }
    }
    return middleOf(l, u);
}  

int main (void)
{
    findRootBetween(-3.0, 5.0);
}