This isn't a "clever one-liner" it is a clear and precise syntax for expressing the operation the machine actually performs.

while(copy(current(stream_a), current(stream_b)) and not end_of_stream(stream_a))

You might prefer the above, but then, that's every other major language. The beauty of C is that the above code has to compile to something like the C version. C just allows you to actually express it