Java Bloopers

Here are two very tricky problems that people in our class had.

Exponentiation

What should the output of loop(5) be?

public static void loop(int y)
{
    for (int k = 0; k < (y^2); k++) {
        System.out.println(k);
    }
}

Explain:

DemoBlooper.loop(5);
0 1 2 3 4 5 6 

Uh-oh:

DemoBlooper.loop(7);
0 1 2 3 4 

I’ll leave it a mystery for now. If you want the compiler to give you a hint, remove the parentheses around y^2.

Conditionals

The following code is supposed to examine the neighbors of the element row=r, col=c in the array temp. If the element is 1 but it has less than 2 or more than 3 neighbors, it becomes 0. If the element is 0 but has 3 neighbors, it becomes 1.

int nextalive = countnextalive(size, r, c, temp);
if(temp[r][c] == 1)
    if(nextalive < 2 || nextalive > 3)
        nums[r][c] = 0;
else
    if(nextalive == 3)
        nums[r][c] = 1;

The code has a bug in it… any ideas? You’ll probably need to test it to figure out what’s wrong.