Displaying recursion steps.

[medosz]

I would like to print the local variable and the recursive call parameter for each recursive call. Cout is not a return type so I can not use it in this return statement. How can I put a new return statement to print these? I am more interested in solving the dispay problem than to see the recursion steps.

 #include <iostream>
#include <iomanip>
using namespace std;

unsigned long factorial(unsigned long);

int main(){
  for(unsigned long counter{0}; counter<=10; counter++){
      cout << setw(2) << counter << "! = "
      << factorial(counter) << endl;
  }
}

unsigned long factorial(unsigned long number){
    if(number <=1){
        return 1;
    }
    else{
        return number * factorial(number - 1);
    }
}

[keskiverto]

You have tried printing?

#include <iostream>
#include <iomanip>
using namespace std;

unsigned long factorial(unsigned long);

int main(){
  for(unsigned long counter{0}; counter<=10; counter++){
      cout << setw(2) << counter << "! = "
        << factorial(counter) << endl;
  }
}

unsigned long factorial(unsigned long number){
    cout << ' ' << number; // print
    if(number <=1){
        return 1;
    }
    else{
        return number * factorial(number - 1);
    }
}

How did it fail?


Or would you rather store data and print it later?

#include <iostream>
#include <iomanip>
#include <vector>
using namespace std;

unsigned long factorial(vector<unsigned long>&, unsigned long);

int main(){
  for(unsigned long counter{0}; counter<=10; counter++){
    vector<unsigned long> calls;
    cout << setw(2) << counter << "! = "
        << factorial(calls, counter) << endl;
    for ( auto c : calls ) cout << ' ' << c;
    cout << '\n';
  }
}

unsigned long factorial(vector<unsigned long>& v, unsigned long number){
    v.emplace_back( number );
    if(number <=1){
        return 1;
    }
    else{
        return number * factorial(v, number - 1);
    }
}

[dutch]

#include <iostream>
#include <iomanip>
using namespace std;

template<typename ...Args>
void p(int depth, Args&&... args) {
    cout << setw(depth * 4) << "";
    (cout << ... << args) << '\n';
}

unsigned long factorial(unsigned n, unsigned depth=0) {
    if (n <= 1) {
        p(depth, n, " (1)");
        return 1;
    }
    else {
        p(depth, n);
        auto x = factorial(n - 1, depth + 1);
        p(depth, n, " (", n * x, ')');
        return n * x;
    }
}

int main(){
    int n = 10;
    auto f = factorial(n);
    cout << setw(2) << n << "! = " << f << '\n';
}

10
    9
        8
            7
                6
                    5
                        4
                            3
                                2
                                    1 (1)
                                2 (2)
                            3 (6)
                        4 (24)
                    5 (120)
                6 (720)
            7 (5040)
        8 (40320)
    9 (362880)
10 (3628800)
10! = 3628800