FLTP_CHAR_CONVERSION

data: input      type f,
        output(22) type c.
 
 
    input = '3.0000000000001098E-03'.

*first method
    write input to output exponent 0 decimals 18.

*second method
*    call function 'FLTP_CHAR_CONVERSION'
*      exporting
*        decim = 18
*        expon = 0
*        input = input
*        ivalu = 'X'     "abap_true'
**       MASKN = ' '
*      importing
*        flstr = output.
    write:/ output.