1. Week 4: Organizational matters Register yourself to CIMS (Course Information and Management System) by clicking on Homework at hidiv.cc.itu.edu.tr/~F90 n Do not send your homeworks to me by e- mail! n Deadline for HW1 is postponed to March 10

2. Week 4 Let’s start with a review

3. Procedures n Divide and rule! Main program Procedure 1 Procedure 2 Procedure 3

4. Programs and modules n Main program unit program name use statements. Specification statements. Executable statements. end program name

5. Programs and modules n Module program unit module name use statements. Specification statements. contains Procedure definitions. end module name

6. Procedures n Divide and rule! Main program Procedure 1 Procedure 2 Procedure 3

7. Procedures n Procedures - origin –“Write your own” (homemade) –Intrinsic (built-in, comes with F ) sin(x), cos(x), abs(x), … –Written by someone else (libraries) n Procedures (subprograms) - form –Functions –Subroutines

8. Procedures n The main program amd any subprogram need never be aware of the internal details of any other program or subprogram! Main program Procedure 1 Procedure 2 Procedure 3

9. Functions function cube_root result(root) ! A function to calculate the cube root of a positive real number ! Dummy argument declaration real, intent(in) :: x ! Result variable declaration real :: root ! Local variable declaration real :: log_x ! Calculate cube root by using logs log_x = log(x) root = exp(log_x/3.0) end function cube_root

10. Functions function name (d1, d2, …) result (result_name) Specifications part Execution part end function name n Variables –Internal (local) variables –Result variable (keyword result ) –Dummy argument (keyword intent(in) ) attribute

11. Functions n No side effects! Restrictions on the statements that can appear within a function

12. Subroutines subroutine roots (x, square_root, cube_root, fourth_root, & fifth_root) ! Subroutine to calculate various roots of positive real ! Number supplied as the first argument, and return them in ! the second to fifth arguments ! Dummy argument declarations real, intent(in) :: x real, intent(out) :: square_root, cube_root, & fourth_root, fifth_root ! Local variable declaration real :: log_x ! Calculate square root using intrinsic sqrt square_root = sqrt(x) ! Calculate other roots by using logs log_x = log(x) cube_root = exp(log_x/3.0) fourth_root = exp(log_x/4.0) fifth_root = exp(log_x/5.0) end subroutine roots

13. Subroutines call name (arg1, arg2, …) n intent(in), intent(out), intent(inout)

14. Arguments n Actual arguments in the calling program n Dummy arguments in the subroutine or function n The order and types of the actual arguments must correspond exactly with the order and types of the corresponding dummy arguments

15. Objects n Local variables vs. global variables private vs. public objects

16. Saving the values of local objects n Local entities within a procedure are not accessible from outside that procedure n Once an exit has been made, they cease to exist n If you want their values to ‘survive’ between calls, use real, save :: list of real variables

17. New stuff... Design Making Flow Control

18. Choice and decision-making If criterion 1 then action 1 but if criterion 2 then action 2 but if criterion 3 then action 3 otherwise action 4

19. Choice and decision-making if (criterion_1) then action_1 else if (criterion_2) then action_2 else if (criterion_3) then action_3 else action_4 endif

20. Logical expressions n Logical variables + logical constants + logical operators n Two values: true or false

21. logical variables n logical :: var_1, var_2, … n Logical valued functions function name(arg1, …) result logical_variable logical :: logical_variable

22. Logical operators L1L2L1.or. L2L1.and. L2 true true truefalsetruefalse falsetruetruefalse falsefalsefalsefalse L1.not. L1 truefalse falsetrue

23. Logical operators L1L2L1.eqv. L2L1.neqv. L2 true true true false truefalsefalsetrue falsetruefalsetrue falsefalsetruefalse

24. Relational operators a < b less than a <= b less than or equal to a > b greater than a >= b greater than or equal a == b equal a /= b not equal

25. Examples n (a d) n (x<=y).and. (y<=z) n.not. (a<b).eqv. (x<y) n a<b.neqv. x<y

26. Logical operator priorities n OperatorPriority.not. highest.and..or..eqv. and.neqv. lowest

27. The if construct if (logical expression) then block of F statements else if (logical expression) then block of F statements else if (logical expression) then block of F statements else block of F statements endif

28. Simple if construct if (logical expression) then block of F statements endif

29. Comparing numbers n Accuracy/round-off –Number of significant digits for real numbers n Do not test whether two numbers are equal n Test whether their difference is acceptably small

30. The case construct select case (case_expression) case (case_selector) block_of_statements... case default block_of_statements end select

31. The case construct n Case expression: –either integer or character expression n Case selector: –case_value case_expression = = case_value –low_value: low_value <= case_expression –:high_value case_expression <= high_value –low_value:high_value low_value <= case_expression.and. case_expression <= high_value

32. Homework n Due on March 15 n from Ellis & Philips –4.11 –5.11