c++ return two arrays from the function - c++

Question

I find a solution to the equation using the bisection method.
And I need to find the value of a and b on some iterations. Therefore, I made two arrays for these points, respectively.
in order to "pull out" the number of iterations from the function, I had no problems. They are displayed on the screen. But how do I "pull out" these two arrays?Please tell me how to do it. Thank you in advance!
double f1(double x){
return x*x-5*sin(x);
}
double f2(double x){
return exp(x)-pow(10,x);
}
double f3(double x){
return sin(x)-x+0.15;
}
double f4(double x){
return x-pow(9+x,0.5)+x*x-4;
}
double dihotom (double a , double b , double e , double(*fp)(double),int &iter,double &points_a[],double &points_b[]){
double c , fc , fa = fp(a);
iter=(log10((b-a)/e))/log10(2);
int step = iter/3;
int step_current = step;
int it=0;
int k=0;
do{
c=(a+b)/2;
fc=fp(c);
if (fa*fc<=0) b = c ; else a = c;
it++;
if(it==step_current){
points_a[k]=a;
points_b[k]=b;
k++;
step_current=step_current+step;
}
fa=fp(a);
printf ("it %d: a = %lf,b = %lf\n",iter,a,b);
}while (fabs(a-b)>=e);
return c;
}
int main(int argc, char *argv[]) {
int int_s=0;
double points_a[3];
double points_b[3];
double k3= dihotom (0.5,1,0.0001,f3,int_s,points_a[3],points_b[3]);
printf("For F3 - root = %lf, F3(%.2lf)=%lf ;iter =%d\n", k3, k3 ,f3(k3),int_s);
int i=0;
for(i=0;i<3;i++){
printf("step : %d , a: %lf, b: %lf ", i,points_a[i],points_b[i]);
}
return 0;
}

Answer 1

In your case, you should take the arrays by reference:
double dihotom(double a, double b, double e, double (*fp)(double), int &iter,
double (&points_a)[3], double (&points_b)[3]) {
// ^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^^
You could also let the arrays decay into pointers:
double dihotom(double a, double b, double e, double (*fp)(double), int &iter,
double points_a[], double points_b[]) {
or
double dihotom(double a, double b, double e, double (*fp)(double), int &iter,
double* points_a, double* points_b) {
But by taking them by reference, you make sure that you only accept arrays of the correct size.
In either case, the call to the function will simply be:
double k3 = dihotom(0.5, 1, 0.0001, f3, int_s, points_a, points_b);
Demo

Answer 2

If you want to return two arrays from a function then make a struct with two vectors. Something like this. The way you are doing it is harder to maintain, who will allocate the arrays and delete them for example?
// todo for you : create better names then points_a and points_b
struct my_result_t
{
std::vector<double> points_a;
std::vector<double> points_b;
};
my_result_t function();
{
my_result_t result;
result.points_a.push_back(1.0);
result.points_b.push_back(2.0);
return result;
}
int main()
{
auto result = function();
std::cout << result.points_a[0];
}