How to identify INFINITY or NAN

 practice example

program main

integer ihuge,inan

real ahuge,ahuge2

double precision dahuge

real anan,anan2,binf

anan=sqrt(-1.0)

print *, 'anan=',anan

binf=1.0/0.0

print *, 'binf=',binf

ihuge=huge(1)

print *, 'ihuge=',ihuge

ahuge=huge(1.0)

print *, 'ahuge=',ahuge

ahuge2=huge(1.0d0)

print *, 'ahuge2=',ahuge2

dahuge=huge(1.0d0)

print *, 'dahuge=',dahuge

anan2=ahuge2/binf

print *, 'anan=',anan2

if (ahuge2.gt.ahuge) then

print *,'ahuge2 is infinity'

else

print *,'ahuge2 is a valid number'

endif

if(anan.ne.anan) then

print *,'anan is NAN'

else

print *,'anan is a valid number'

endif

if(anan2.ne.anan2) then

print *,'anan2 is NAN'

else

print *,'anan2 is a valid number'

endif

pause

stop

end

Output:

D:\workdir\temp\inf_nan>inf_nan.exe

anan=            NaN

binf=       Infinity

ihuge=  2147483647

ahuge=  3.4028235E+38

ahuge2=       Infinity

dahuge=  1.797693134862316E+308

anan=            NaN

ahuge2 is infinity

anan is NAN

anan2 is NAN

Fortran Pause - Enter command or to continue.