Question

how to get all the possible ways in which positions of array can be picked?
for ex for array of size 2 there are 3 possibilities first element, second element and both the elements.
for array of size 3 possibilities are first, second, third,first and second, first and third, second and third,and finally first second and third.
i want a simple nested loops for it..

Answer 1

Nested loops aren’t really the answer here, because the depth of nesting would depend on the size of the array.

So you think in binary: the subsets of the size-N array correspond to the non-zero binary numbers of the right length, so do something like

for (int subset_c = 1; subset_c < (1<<N); subset_c++)
{
    { start thinking about a new subset }
    for (int j=0; j<N; j++)
    {
         if ((subset_c>>j)&1) { the subset should contain array[j] }
    }
}