sum in f90 not working?

[xrayspex1]

hi all, i'm a complete newbie to fortran - if someone can take 30 seconds to look at the short code below and tell me why it prints the wrong sum of two numbers, i'd be very gratefull, because i'm freaking out already...

CODE:
program temp
implicit none

real,external :: add
real :: y

y = add(3,4)
print *,y

end program temp

real function add(x,n)
implicit none
real, intent(in) :: x
real, intent(in) :: n

add = x+n

end function add

OUTPUT:
9.8090893E-45
Press any key to continue

any ideas?????

 

[xwb]

It is because there is no prototyping in Fortran so it doesn't really know what the parameter types are. Try

   y = add (3.0, 4.0)

Reason why you're getting 9.8E-45 is because 3 and 4 are combined into one floating point number. The other one is just a random number on the stack.

 

[ArkM]

Use INTERFACE statement for prototyping in F90+.
See, for example:

http://www.pv.infn.it/sc/f90/f_ug1/pgwproto.htm

 

[xwb]

Nice one Arkm - I'd completely forgotten about INTERFACE.

 

[xrayspex1]

great, thanks a lot guys!