Week 4:Organizational matters

Register yourself to CIMS (Course Information and Management System)by clicking on Homework athidiv.cc.itu.edu.tr/~F90

Do not send your homeworks to me by e-mail!

Deadline for HW1 is postponed toMarch 10

Week 4

Let’s start with a review

Procedures

Divide and rule!

Main program Procedure 1

Procedure 2 Procedure 3

Programs and modules

Main program unit

program nameuse statements...Specification statements...Executable statements...

end program name

Programs and modules

Module program unit

module nameuse statements...Specification statements...

containsProcedure definitions...

end module name

Procedures

Divide and rule!

Main program Procedure 1

Procedure 2 Procedure 3

Procedures

Procedures - origin– “Write your own” (homemade)– Intrinsic (built-in, comes with F )

•sin(x), cos(x), abs(x), …

– Written by someone else (libraries) Procedures (subprograms) - form

– Functions– Subroutines

Procedures

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 2Procedure 3

Functionsfunction 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

Functions

function name (d1, d2, …) result(result_name)

Specifications part

Execution part end function name Variables

– Internal (local) variables– Result variable (keyword result)– Dummy argument (keyword intent(in))

attribute

Functions

No side effects!

Restrictions on the statements that can appear within a function

Subroutinessubroutine 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

Subroutines

call name (arg1, arg2, …) intent(in), intent(out), intent(inout)

Arguments

Actual arguments in the calling program Dummy arguments in the subroutine or

function The order and types of the actual

arguments must correspond exactly with the order and types of the corresponding dummy arguments

Objects

Local variables vs. global variables private vs. public objects

Saving the values of local objects

Local entities within a procedure are not accessible from outside that procedure

Once an exit has been made, they cease to exist

If you want their values to ‘survive’ between calls, usereal, save :: list of real variables

New stuff...

Design Making

Flow Control

Choice and decision-making

If criterion 1 thenaction 1

but if criterion 2 thenaction 2

but if criterion 3 thenaction 3

otherwiseaction 4

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

Logical expressions

Logical variables + logical constants + logical operators

Two values: true or false

logical variables

logical :: var_1, var_2, … Logical valued functions

function name(arg1, …) result logical_variable

logical :: logical_variable

Logical operators

L1 L2 L1 .or. L2 L1 .and. L2

true true true true

true false true false

false true true false

false false false false

L1 .not. L1

true false

false true

Logical operators

L1 L2 L1 .eqv. L2 L1 .neqv. L2

true true true false

true false false true

false true false true

false false true false

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

Examples

(a<b) .or. (c>d) (x<=y) .and. (y<=z) .not. (a<b) .eqv. (x<y) a<b .neqv. x<y

Logical operator priorities

Operator Priority

.not. highest

.and.

.or.

.eqv. and .neqv. lowest

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

Simple if construct

if (logical expression) then

block of F statements

endif

Comparing numbers

Accuracy/round-off– Number of significant digits for real

numbers Do not test whether two numbers are

equal Test whether their difference is

acceptably small

The case construct

select case (case_expression)

case (case_selector)

block_of_statements

...

case default

block_of_statements

end select

The case construct Case expression:

– either integer or character expression 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

Homework

Due on March 15 from Ellis & Philips

– 4.11– 5.11