int test_bit(string str, int n)
Return 0 or 1 of bit n was set in string str.
Each character contains 6 bits. So you can store a value
between 0 and 63 in one character (2^6=64). Starting character
is the blank " " which has the value 0. The first character in
the string is the one with the lowest bits (0-5).
Returns 1 because "_" stands for the number 63 and therefore
the 6th bit is set.
Returns 0 because " " stands for 0 and no bit is set.
set_bit(E), clear_bit(E), last_bit(E), next_bit(E), count_bits(E),
and_bits(E), or_bits(E), xor_bits(E), invert_bits(E), copy_bits(E)