Ecvt converts the value to a null-terminated string of ndigit ASCII digits and returns a pointer thereto. The
position of the decimal point relative to the beginning of the string is stored indirectly through decpt (neg-
ative means to the left of the returned digits). If the sign of the result is negative, the word pointed to
by sign is non-zero, otherwise it is zero. The low-order digit is rounded.
Fcvt is identical to ecvt, except that the correct digit has been rounded for Fortran F-format output of the
number of digits specified by ndigits.
Gcvt converts the value to a null-terminated ASCII string in buf and returns a pointer to buf. It attempts to
produce ndigit significant digits in Fortran F format if possible, otherwise E format, ready for printing.
Trailing zeros may be suppressed.