Some minor things, but may still be worth mentioning:

Whenever `std::endl` is used, the buffer gets flushed, which can add to performance a bit, especially if it's done multuple times.

In order to get a newline without this added flush, use `"\n"` within an output statement:

    std::cout << "\n";

Also, consider adding a bit more whitespace within the multiple loop statements for added readability:

    for (int a = 1; a <= 100; a++)