It seems that 's' is a matrix which is created with all the possible permutations between 2 different numbers in the vector 'myints'.
's' is a matrix of size 2 x 90, where 90 is the number for permutations which you can create.
The matrix 's' will look as follows:
{0, 1}
{0, 2}
:
:
{0, 9}
{1, 0} // notice that there is no permutation of {1, 1}, {2, 2} ... {9, 9}
{1, 2}
:
:
{9, 8}
Looking at the nested-loop code:
for(auto c: s){
for (auto i: c)
cout << i << " ";
cout << endl;
'auto' simply iterate over the elements of a vector.
The first for-loop will iterate through all the permutation pairs in s. And the nested for-loop will iterate through the permutation pair items, 'c' is a the parameter which represents a single permutation pair and 'i' represents one of the (two) items in 'c'.