Question

What I want to do is convert a string such as
“a4b2f0” into “f0b2a4”
or in more simple terms:

turning "12345678" into "78563412"

The string will always have an even number of characters so it will always divide by 2. I’m not really sure where to start.

Answer 1

One simple way to do that is this:

std::string input = "12345678";
std::string output = input;
std::reverse(output.begin(), output.end());
for(size_t i = 1 ; i < output.size(); i+=2)
    std::swap(output[i-1], output[i]);
std::cout << output << std::endl;

Online demo

A bit better in terms of speed, as the previous one swaps elements twice, and this one swap each pair once:

std::string input = "12345678";
std::string output = input;
for(size_t i = 0, middle = output.size()/2, size = output.size(); i < middle ; i+=2 )
{
     std::swap(output[i], output[size - i- 2]);
     std::swap(output[i+1], output[size -i - 1]);
}
std::cout << output << std::endl;

Demo