is the output correct

[locy]

int n = 20;

while(n>0)
n/=2;
std::cout<<n * n<<std::endl;


is this correct if i divide 20/2 = 10
and multiply 10*10 as the output

[Extremist]

The output of your code will be 0;
The while will continue until n = 0;

n = 20 while makes n = 10
n = 10 while makes n = 5
n = 5 while makes n = 2
n = 2 while makes n = 1
n = 1 while makes n = 0

perhaps what you mean to do is:

int n = 20;
    while(n>0)
    {
        n/=2;    
        std::cout <<n*n<< std::endl;
    }
 

Output will be
100
25
4
1
0