This function is different to CDEC$ in that it always prints the given value in exponential format. This means that there is always only one character to the left of the decimal point (plus any sign), and ndp (number of decimal places) states how many characters should be to the right of the decimal point.
FEXP$ does not assume that value is an integer and therefore also caters for floating point values. The length of the field must be at least ndp+7, otherwise an empty string is returned.
If necessary, values are rounded up or down to fit in the specified ndp number of decimal places.
will print -1.0023E+02
will print 1.0024E+02