Question

I am doing a book exercise regarding the Ackermann function.

I have one question though. If I declare result but do not initialise it, the compiler complains that “variable result might not have been initialised”.

int result;

When I set it to default to 0, it does not complain.

int result = 0;

I thought that when one declares a variable with type int it defaults to 0 automatically.

Here’s the complete code:

public class Ackermann {
   public static int ack(int m, int n) {
     int result = 0;
     //int result;
     if (m == 0)
        result = n + 1;
     else if(m > 0 && n == 0)
        result = ack(m-1, 1); 
     else if(m > 0 && n > 0)
        result = ack(m-1, ack(m, n-1));
     return result;
   }   

   public static void main(String[] args) {
      System.out.println(ack(3, 3));  
   }   

}

Answer 1

Local variables are not initialized with default values. See the language specs for the ground truth.