http://gcc.gnu.org/onlinedocs/gfortran/Implicitly-convert-LOGICAL-and-INTEGER-values.html
INTEGER :: i = 1 IF (i) PRINT *, 'True' The program is rejected here with gfortran 4.1, 4.2 and 4.3 using -std=legacy. -- Summary: Doc error or rej.valid vendor extension: Integer as logical in IF expressions Product: gcc Version: 4.3.0 Status: UNCONFIRMED Keywords: documentation Severity: normal Priority: P3 Component: fortran AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: burnus at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34532