The flow control: for

I have problem tu understand the iteration of the flow control.

Someone can help me to understand the iteration of this code?

Thank in advance!

Actually the above code will not compile because the variable j is declared in the inner loop and you are trying to use it in the outer loop. The compiler will say j cannot be resolved

Once you post the corrected code, let us know which part you cannot understand

As the others have said, line 7 contains an error, because the variable j is out of scope at that point - that is, the variable j doesn't exist anymore, it only exists in lines 4-6. Suppose that we comment out line 7.

The for keywords creates a loop. In your example, you have a loop over variable i going from 0 until and including 9. Inside that loop, there is a nested loop over variable j. Note that the condition for the nested loop is j<0. That means the loop will never iterate, because j is never less than 0.

See Control Flow Statements in Sun's Java tutorials to learn about the for statement and other control flow keywords of Java.

Sorry guys...
This is the corret code!!
I have to understand how this working!

Thanks again!

int[][] a1 = {{1,2,3},{4,5,6},{7,8,9}};
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
System.out.print(a1[j][i]);
}
}

Hi
Lorenzo
first the outer loop will run once for value of i and the inner will run thrice for value of j
the again the loop will increment the value of i to 1 and the inner will run thrice for value of j
this will continue until the value of i is reache to 3 and loop will exit.
output is 147258369
hope this helps.

Hi Lorenzo,

for this type of questions, I generally recommend to write down the whole iteration steps on a piece of paper, for example like this:

i----------j----------a1[j][i]
0-----------0---------------1
0-----------1---------------4
0-----------2---------------7
1-----------0---------------2
1-----------1---------------5
1-----------2---------------8
2-----------0---------------3
2-----------1---------------6
2-----------2---------------9

The array a1 can be read like this:
a1[0] = {1, 2, 3};
a1[1] = {4, 5, 6};
a1[2] = {7, 8, 9};

Let's take the case where i=1 and j=2:
a[j][i] -> a[2][1] = 8

Hope this helps!
I advise to do like this even in the real exam, because the only fact of writing down can prevent you from the awkward oversights.
The devil is in the details ;-)

Thank you guys!!

Your tips are very important for me!!

I'm studying to become like you...a Java Programmer Certified!! ;-)