calling_func.f90

program calling_func
implicit none

   real :: a, b
   a = 2.0
   b = 3.0

   Print *, "Before calling swap"
   Print *, "a = ", a
   Print *, "b = ", b

   call swap(a, b)

   Print *, "After calling swap"
   Print *, "a = ", a
   Print *, "b = ", b

end program calling_func


subroutine swap(x, y) 
implicit none

   real :: x, y, temp   

   temp = x  
   x = y 
   y = temp  

end subroutine swap