Integer to binary(Using recursivity)

[romulosd]

I'm trying to develop a recursive function to convert an integer number into binary and putting the result into a vector using the following logic:
Every function call, divide the number by 2, if the remainder is equal to 0, insert a 0 in vector, if not, put one in the vector.

Soon after when the function ends, I show the contents of the vector.
However, nothing is displayed on the screen.
Why?

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <vector>
using namespace std;

void itob(short n,vector<int> binary);

int main()
{

    short n;
    vector <int> binary;
    cin>>n;
    itob(n, binary);
    for(int i = 0; i < binary.size(); i++)
    {
        cout<<binary.at(i)<<" ";
    }    

    return 0;
}
void itob(short n,vector<int> binary)
{
    if(n > 0 )
    {
        if(n % 2 == 0)
        {
            binary.push_back(1);
        }
        else
        {
            binary.push_back(0);
        }
        itob(n-1,binary);
    }
}

[D80DSL3A]

You're passing the vector by value so its contents can't be modified by the function. The function is working with a copy.
Pass the vector by reference instead:
void itob(short n,vector<int>& binary);// note the &

[romulosd]

Thank you.
Why when I pass the vector as parameter, it does not automatically pass by reference? Like an array?
Why is not the same thing?

[LB]

Arrays don't follow the same rules as everything else in C++ - don't base any assumptions on how arrays behave ;)

Arrays are generally passed by pointer, not by reference, without you knowing it. You can force them to be passed by reference, though.

[romulosd]

Would it make any difference?
Passing an array by pointer or reference?

[condor]

@romulosd

I'm afraid that the recursive function is wrong:

1. the vector must store the remainders modulo 2, (n % 2 without if test)
2. recursive process must be resumed with n / 2 not with n - 1

and so the function will be as follows:

void itob(int n, std::vector<int> &binary)
{
	if(n > 0)
	{
	   binary.push_back( n % 2);
	   itob(n / 2, binary);
	}
}

and lines 16 - 19 (your code) must read the vector from the end to the beginning.

[romulosd]

Yes @condor
i already solve this problem.
Thanks!

void itob(short n, vector<int> &bin)
{
    int d = n;

    if (n > 1)
    {
        d = n % 2;
        itob(n / 2, bin);
    }
    bin.push_back(d);
}

[condor]

Congratulations! Happy programming! ;)

[romulosd]

:D