https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69456
--- Comment #2 from kargl at gcc dot gnu.org --- (In reply to Josiah Schwab from comment #0) > > I read the code for the function parse_real in libgfortran/io/list_read.c > and this behavior appears to exist because the value '1+1' is permitted as a > shorthand for '1e+1'. This was also surprising to me. > > I read the Fortran 2008 specification. I had difficulty fully understanding > it, but I failed to find a place where it said that exponent-letter can be > legally omitted. A look at the list of gfortran vendor extensions as well > as a web search also failed to provide additional information. > > See Table 10.1, "E and D Exponent Forms" in Fortran 2008 standard.