Using markdown
#include <iostream>
using namespace std;
void recursion(int i)   {
    if(i == 10)
        return;
    cout << i << " ";
    recursion(i+1);
    cout << i << " ";
}
int main()  {
    recursion(1);
    return 0;
}
Using Control K shows corrected code
#include <iostream>
using namespace std;
void recursion(int i)   {
    if(i == 10)
        return;
    cout << i << " ";
    recursion(i+1);
    cout << i << " ";
}
int main()  {
    recursion(1);
    return 0;
}