Finds the index of the first bit set in a string.
    Format
      #include  <strings.h>
      int ffs  (int iteger);
1 – Argument
 integer
    The integer to be examined for the first bit set.
2 – Description
    The ffs function finds the first bit set (beginning with the
    least significant bit) and returns the index of that bit. Bits
    are numbered starting at 1 (the least significant bit).
3 – Return Values
    x                  The index of the first bit set.
    0                  If index is 0.