public class testing
{
public static void printnum(int a)
{
System.out.println( a);
if(a <= 3)
{
System.out.println("recursed");
printnum(a+1);
}
System.out.println( a);
}
public static void main(String...s)
{
printnum(1);
}
}
output:
1
2
3
3
2
1
I expected the program to end at last 3 but I do not understand where are the next '2' and '1' coming from? How and why is it decrementing?
You've got two calls to System.out.println(a). You'll find it much easier to understand if you differentiate between them:
public static void printNum(int a)
{
System.out.println("Before recursion: " + a);
if(a <= 3)
{
System.out.println("Recursing");
printNum(a + 1);
}
System.out.println("After recursion: " + a);
}
Basically, your calls nest - your most deeply nested call will print:
Before recursion: 4
After recursion: 4
... and then it will return back to the call to printNum(3), which will print:
After recursion: 3
and return to the call to printNum(2), which will print
After recursion: 2
etc.
Now would also be a good time to learn how to use a debugger to step through your code, look at the stack at every point, etc.
If you expect it to end at 3 then please remove the second
System.out.println( a);
The out put you see is correct and not unexpected as when it is greater than 3 the it return the stack call and prints in in the reverse order.
What you getting as output is correct according to your code. You get extra lines due to the your second System.out.println("After recursion: " + a);
