for循环的迭代次数

Question

I can't figure out for the following for-loop, how many time it will execute? It seems to me that it will never stop running as i will never be less than 0. But I know that i is an int , so I'm quite confused about when the loop will stop. Many thanks for your help!

for (int i = n; i > 0; i = i/2) {
    System.out.println(s);
}

Also is the complexity log2(n) ?

Answer 1

It depends.

For n <= 0 it will be never inside.

For n > 0 it will be executed log2(n) + 1 times

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n = 8

It will be invoked for i = 8, 4, 2, 1 so finally, 3 + 1 = log2(8) + 1

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It also works with @Keppil test:

30 < log2(2147483648 - 1) < 31

and the result set has 31 elements.

Answer 2

It will run for a number of iterations,given by log2(n) , the last one being when i=1. When the condition is checked the next time, i = 1/2 in int, which evaluates to zero and violates the condition and exits the loop. So it depends on the value of n .

Answer 3

Just modify your code a little bit to see what happens there:

int n = 50;
for (int i=n; i>0; i=i/2){
    System.out.println("i: " + i);
}
System.out.println("1/2 in Java is: " + 1/2);

The output is:

i: 50
i: 25
i: 12
i: 6
i: 3
i: 1
1/2 in java is: 0

Now you should be able to understand why this loop ends.