select to_char(a, '99D90') test1,
    to_char(a, '90D90')    test2,
    to_char(a, 'FM90D99')  test3,
    rtrim(to_char(a, 'FM90D99'), to_char(0, 'D')) test4
from (
    select 50 a from dual
    union all select 50.57 from dual
    union all select 5.57 from dual
    union all select 0.35 from dual
    union all select 0.4 from dual
    union all select 0.80 from dual
    union all select .88 from dual
)
order by a;

TEST1  TEST2    TEST3  TEST4
------ ------   ------ ------
   .35   0.35   0.35   0.35
   .40   0.40   0.4    0.4
   .80   0.80   0.8    0.8
   .88   0.88   0.88   0.88
  5.57   5.57   5.57   5.57
 50.00  50.00   50.    50
 50.57  50.57   50.57  50.57

SQL> WITH DATA AS(
  2  select 50 a from dual
  3      union all select 50.57 from dual
  4      union all select 5.57 from dual
  5      union all select 0.35 from dual
  6      union all select 0.4 from dual
  7      UNION ALL SELECT 0.80 FROM dual
  8      UNION ALL SELECT .88 FROM dual
  9  )
 10  SELECT
 11    CASE
 12      WHEN TRUNC(A) = 0
 13      THEN ltrim(to_char(a, '0D99'), ' ')
 14      ELSE TO_CHAR(a)
 15    END text
 16  FROM DATA;

TEXT
----------------------------------------
50
50.57
5.57
0.35
0.40
0.80
0.88

7 rows selected.

SQL>