integral equation: automatic integration step

double getIntegral(double (*f)(double), double a, double b, long n, double eps, double step) {
    double x, y, z;
    double integral = 0;
    do{
        x = integrate(f, a, a+step, n);
        y = integrate(f, a, (a+step)/2, n);
        z = integrate(f, (a+step)/2, a+step, n);
        if(fabs(x-(y+z)) < eps){
            a+=step;
            integral+=x;
        }
        n*=2;
    }while(a+step < b);
    return integral;
}