Segmentation fault in static member function c++

Question

class Adder {
public:
    static int Solve(int a, int b) {return a + b;}
};

class Substructor {
public:
    static int Solve(int a, int b) {return a - b;}
};

class Comparer {
public:
    static bool Solve(int a, int b) {return a < b;}
};

class If {
public:
    static int Solve(bool term, int a, int b) {return term ? a : b;}
};

class Fibo {
public:
    static int Solve(int num) {
      int res =
      If::Solve(
        Comparer::Solve(num, 2),
        1,       
        Adder::Solve(
          Fibo::Solve(Substructor::Solve(num, 1)),
          Fibo::Solve(Substructor::Solve(num, 2))
        )
        
      );
      return res;
    }
};

int calc(int x) {
  return Fibo::Solve(x);
}

#include <iostream>
int main() {
  std::cout << calc(5) << '\n';
  return 0;
}

This code leads to segmentation fault. I tested all classes separately, write recursive fibo static member function without other static member functions and it works. While combined it crushes. How to fix it and why it crush?

Answer 1

The problem arises here:

class Fibo {
public:
    static int Solve(int num) {
      int res =
      If::Solve(
        Comparer::Solve(num, 2),
        1,       
        Adder::Solve(
          Fibo::Solve(Substructor::Solve(num, 1)),
          Fibo::Solve(Substructor::Solve(num, 2))
        )
      );
      return res;
    }
};

In the If::Solve() sentence, what you expected maybe, if Comparer::Solve(num, 2) checks that num<2, return 1 and do not evaluate the remaining expressions Fibo::Solve(Substructor::Solve(num, 1)) and the second one, it will not work as you expected. To evaluate If::Solve() , every arguments must be evaluated before to pass to If::Solve() . As it evaluates again and again recursively, stack overflow occurs, therefore program terminates. If you really wish to make it run, modify like this:

class Fibo {
public:
    static int Solve(int num) {
        if (Comparer::Solve(num, 3)) {
            return 1;
        }
        else return Adder::Solve(
            Fibo::Solve(Substructor::Solve(num, 1)),
            Fibo::Solve(Substructor::Solve(num, 2))
        );
    }
};

This guarantees that if num is 1 or 2, return 1 and does not evaluates remaining expressions.