Java - Recursion sum of number and how it work
<p>I am trying to write a recursive function that when I call with number 5 for example then the function will calculate the sum of all digits of five. 
1 + 2 + 3 + 4 + 5 = 15</p>

<p>The current code always returns 0, how can the amount each time the n? </p>

<pre><code>public class t {
public static void main(String[] args) {

    System.out.println(num(5));
}

public static int num(int n) {

    int sum = 0;
    sum += n;
    if (n == 0)
        return sum;

    return num(n - 1);

}

}
</code></pre>

<p>thank you.</p>