Thread: Have question on implementing a certain recursive function

First of all, do NOT post complete or partial solutions, only help. Second of all, I am having trouble implementing the recursive function in 2 homework programs I'm doing.

The first one sums multiples of 3, and the second one does combinations (number choose number) but I have no clue how to implement it. I have tried by myself, but both programs are a disaster.

Code:

#include <iostream>
using namespace std;
int sum3s(int sum) {
    if(sum == 1) {
           return 0;
           }
           else if (sum / 3 + 1 && 3 + 2 && 3 + 3 == 3) {
                
                return 1 + 3 + 2 + 3 + 3 + 3 * sum3s(3 * 3 * sum);
}
}
int main ( ) {
    int number;
    cout << "Enter number: ";
    cin >> number;
    cout << "" << endl;
    cout << "The sum is " << sum3s(number);
    cout << ".";
}

Code:

#include <iostream>
using namespace std;
int combinations (int n, int k) {
    if (n == 1) {
          return 1;
          }
          else {
               return combinations(n + k + n + k + n + k);
}
}
int main ( ) {
    int a;
    int b;
    cout << "Enter an Integer: ";
    cin >> a;
    cout << "Enter another Integer: ";
    cin >> b;
    cout << "Combinations( " << a "," << b ")" " = ";
    cout << combinations(a, b);
}

Here is an example:

On the one where I sum multiples of 3, I put in 10 (or any number) and get 0. I should get 18.

The other one just doesn't compile.

Sum of Multiples of 3 (Recursion) - C++ Forum

^ Same question phrased a little better (at least the first question..no idea on the combinations)

The conditional statement you created

Code:

else if (sum / 3 + 1 && 3 + 2 && 3 + 3 == 3)

is equivalent to

Code:

else if ((sum / 3 + 1) != 0 && true && false)

which will be evaluated always as

Code:

else if (false)

What does code in your sig do?