As a GNU extension for backwards compatibility with other compilers,
gfortran allows the implicit conversion of LOGICALs to INTEGERs
and vice versa. When converting from a LOGICAL to an INTEGER, the numeric
.FALSE. is zero, and that of
.TRUE. is one. When
converting from INTEGER to LOGICAL, the value zero is interpreted as
.FALSE. and any nonzero value is interpreted as
INTEGER*4 i i = .FALSE.