Initial data commit

Task/Call-a-function/Fortran/call-a-function-1.f

@@ -0,0 +1,70 @@
+program main
+implicit none
+integer :: a
+integer :: f, g
+logical :: lresult
+interface
+  integer function h(a,b,c)
+    integer :: a, b
+    integer, optional :: c
+  end function
+end interface
+write(*,*) 'no arguments: ', f()
+write(*,*) '-----------------'
+write(*,*) 'fixed arguments: ', g(5,8,lresult)
+write(*,*) '-----------------'
+write(*,*) 'optional arguments: ', h(5,8), h(5,8,4)
+write(*,*) '-----------------'
+write(*,*) 'function with variable arguments: Does not apply!'
+write(*,*) 'An option is to pass arrays of variable lengths.'
+write(*,*) '-----------------'
+write(*,*) 'named arguments: ', h(c=4,b=8,a=5)
+write(*,*) '-----------------'
+write(*,*) 'function in statement context: Does not apply!'
+write(*,*) '-----------------'
+write(*,*) 'Fortran passes memory location of variables as arguments.'
+write(*,*) 'So an argument can hold the return value.'
+write(*,*) 'function result: ', g(5,8,lresult) , ' function successful? ', lresult
+write(*,*) '-----------------'
+write(*,*) 'Distinguish between built-in and user-defined functions: Does not apply!'
+write(*,*) '-----------------'
+write(*,*) 'Calling a subroutine: '
+a = 30
+call sub(a)
+write(*,*) 'Function call: ', f()
+write(*,*) '-----------------'
+write(*,*) 'All variables are passed as pointers.'
+write(*,*) 'Problems can arise if instead of sub(a), one uses sub(10).'
+write(*,*) '-----------------'
+end program
+
+!no argument
+integer function f()
+f = 10
+end function
+
+!fixed number of arguments
+integer function g(a, b, lresult)
+integer :: a, b
+logical :: lresult
+g = a+b
+lresult = .TRUE.
+end function
+
+!optional arguments
+integer function h(a, b, c)
+integer :: a, b
+integer, optional :: c
+
+h = a+b
+if(present(c)) then
+  h = h+10*c
+end if
+end function
+
+!subroutine
+subroutine sub(a)
+integer :: a
+a = a*100
+write(*,*) 'Output of subroutine: ', a
+end subroutine