Inverse Output of Recursive function C++

Question

I have written a functions that outputs the prime factors of a number entered by the user. The output i am getting is correct, however the output is backwards.

For example the input is 1776: output => 2 x 2 x 2 x 2 x 3 x 37 x

The output I'm looking for is => 37 x 3 x 2 x 2 x 2 x 2

how can I inverse the output and remove the extra multiplication symbol (x) behind 37.

void primefactor(int x)
{
 // initalize a int with a static value of 2
    static int i=2;

// if i less then or equal to x
    if(i<=x)
    {
// while x%i doess equal 0 you have found a factor print factor
        while(x%i ==0)
        {
            cout<<i<<" x ";
// x takes a new value of x / i
            x=x/i;

        }
// increment i and call fuction again
        i++;
        primefactor(x);
    }

}

Answer 1

To remove the trailing x, you can print it out conditionally:

while ((x % i) == 0)
{
    std::cout << i;
    x /= i;
    if (x > 1)
        std::cout << " x ";
}

Also, you can remove the static if you make i be an input parameter instead:

void primefactor(int x, int i = 2)
{
    ...
    primefactor(x, ++i);
    ...
}

Live Demo

But, to reverse the output is a little tricky for this kind of recursion. If you can use an iterative loop instead of a recursive loop, then you can use a local std::vector to accumulate the factors and then reverse their order before printing them, eg:

#include <vector>
#include <algorithm>

void primefactor(int x)
{
    std::vector<int> v;
    int i = 2;
 
    while (i <= x)
    {
        while ((x % i) == 0)
        {
            v.push_back(i);
            x /= i;
        } 
        ++i;
    }
 
    if (!v.empty())
    {
        std::reverse(v.begin(), v.end());
        std::cout << v[0];  
        for(size_t idx = 1; idx < v.size(); ++idx)
            std::cout << " x " << v[idx];
    }
}

Live Demo

But, if you absolutely need a recursive function, you can still use a std::vector, just pass it around to each iteration, eg:

void primefactor_loop(int x, int i, std::vector<int> &v)
{
    if (i <= x)
    {
        while ((x % i) == 0)
        {
            v.push_back(i);
            x /= i;
        }
        primefactor_loop(x, ++i, v);
    }
}
 
void primefactor(int x)
{
    std::vector<int> v;

    primefactor_loop(x, 2, v);

    if (!v.empty())
    {
        std::reverse(v.begin(), v.end());
        std::cout << v[0];  
        for(size_t idx = 1; idx < v.size(); ++idx)
            std::cout << " x " << v[idx];
    }
}

Live Demo