Basic Building Blocks

1
Basic Building Blocks
In all ways of life, the easiest way to solve
most problems is to break them down into smaller
sub_problems and then to deal with each of
these in turn, further sub-dividing these
subproblems as necessary.
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Seven Golden Rules

• Always plan ahead
• Develop in stages
• Modularize
• Keep it simple
• Test throughly
• Document all programs
• Enjoy your programming

3
Programs and modules

• Main program unit
• program name
• use statements
• .
• .
• .
• Specification statements
• .
• .
• .
• Executable statements
• .
• .
• .
• end program name

4
Modules

• Programs for solving complex problems should be
  designed in a modular fashion.
• The problem should be divided into simpler
  subproblems, so that the subprograms can be
  written to solve each of them.
• Every program must include exactly one main
  program and may also include one or more modules.

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Modules

• Modules are a second type of program unit.
• The basic structure of a module is similar to the
  main program unit.
• The initial module statement of each module
  specifies the name of that module based on the F
  language rules.
• A module unit ends with an end module statement
  incuding its name.
• A module does not contain any executable
  statements.
• A module may contain any number of subprograms
  which are seperated from the other statements by
  a contain statement.

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Module program unit

• module name
• use statements
• .
• .
• .
• Specification statements
• .
• contains
• (Procedure definitions)
• subprogram_1
• subprogram_2
• .
• .
• subprogram_n

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Procedures
A special section of program which is, in some
way, referred to whenever required, is known
as a procedure.   Programs      can be
written by the programmer      by some other
person who allows the programmer to use
them     can be a part of the F language itself
(i.e. intrinsic procedures whose names are
reserved words ? must always be written in lower
case).   Subprograms can also be categorized
as   subroutines ( there are 5 intrinsic
subroutines )   functions ( create only
a single result there are 97 intrinsic
functions available in
F )
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Procedures

• Divide and rule!

Main program
Procedure 1
Procedure 3
Procedure 2
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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

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Procedures

• The main program and any subprogram need never be
  aware of the internal details of any other
  program or subprogram!

Main program
Procedure 1
Procedure 3
Procedure 2
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Procedures

• name (argument_1, argument_2, ...)
• Examples
• a b log (c)
• -b sqrt ( b b 4.0 a c)

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Procedures

• A) PROBLEM A farmer has a triangular field
  which he wishes to sow with wheat.
• Write a program that reads the lenghts of the 3
  sides of the field (in meters) and the sowing
  density (in grams per square meters)
• Print the number of 10 kilo bags of wheat he must
  purchase in order to sow the whole field.
• B.) ANALYSIS STRUCTURE PLAN of the PROBLEM
•     read lenghts of the sides of the field ( a,
  b, c ) and calculate the area of the field
• area ( s (s-a)(s-b)(s-c) ) ½
• 2s a b c
•         read the sowing density
•        calculate the quantity of wheat seed
  required
•       calculate the number of 10 kilo bags this
  represents

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C) SOLUTION program wheat_sowing ! This
program calculate quantity of wheat required to
sow a triangular field ! Variable declarations
real a, b, c,s, area, density, quantity
integer num_bags ! read the lengths of the
sides of the field print , type the lengths
of the 3 sides of the field in metres
read , a, b, c ! calculate the area of the
field s 0.5 ( a b c ) area
sqrt( s (s - a)(s - b)(s - c) ) ! read
sowing density print , What is the sowing
density (gms/sq.m) ? read , density !
calculate quantity of wheat and the number of 10
kilo bags ! round up more than 1 kg quantity
density area num_bags 0.0001 quantity
0.9 ! print results print , the area of
the field is , area, sq. metres print ,
and , num_bags, 10 kilo bags will be
required end program wheat_sowing
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Subprograms
Functions Functions may, of course, be provided
by the user and they are normally implemented by
means of an F subprogram which is physically
placed within a module as is explained in
Modules.   On the other hand, very important
principle which applies to all procedures in F is
that the main program and any subprograms need
never be aware of the internal details of any
other program unit or subprograms . A function
subprogram can be called by         the main
program         another subroutine
subprogram         another function
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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
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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

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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

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Subroutines

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

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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

20
Objects

• Local variables vs. global variables
• private vs. public objects

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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, use
• real, save list of real variables

real, savea, b1.23, c Integer, savecount0
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Example
MAIN PROGRAM program .. real Alpha, Beta,
Gamma . . Alpha Fkt ( Beta, Gamma ) . . end
program .    
FUNCTION SUBPROGRAM function Fkt ( x, y ) real
Fkt real x, y Fkt x 2 - 2.5
y 3.7 y 2 x 0.0 end function Fkt
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Example Write a subprogram which calculates the
cube root of a positive real number
MAIN PROGRAM program test_cube_root use
maths real x print , Type a positive real
number read , x Print , The cube root of
,x, is , cube_root(x) . a b cube_root(x)
d . end program test_cube_root
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module maths Publiccube_root contains functi
on cube_root (x) result (root) ! a function
to calculate the cube root of a positive real
number ! Dummy arguments 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) function
cube_root end module maths
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Attributes

• intent (in) the dummy argument only provides
  information to the procedure and is not allowed
  to change its value any way
• intent (out) the dummy argument only returns
  information from the procedure to the calling
  program
• intent (inout) the dummy argument provides
  information in both directions

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Examples of subprograms

• Write a program using either subroutine or
  function
• read the edges of a rectangle,
• write a subprogram which calculate
• area of rectangle

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program
subprogram
!this program is calculates area of a
rectangle !using subroutine program
area_calculation use rec reala,b,al print ,
"enter two edges of the rectangle" read ,
a,b call area (a,b,al) print ,
"a",a print,"b",b print , "area_of_rectangle"
,al endprogram area_calculation
module rec publicarea contains subroutine
area(a,b,al) real, intent(in)a,b real, intent
(out)al alab return endsubroutine area end
module rec
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program
subprogram
!this program is calculates area of a
rectangle program area_calculation use
rec reala,b,al print , "enter two edges of the
rectangle" read , a,b alarea (a,b) print ,
"a",a print,"b",b print , "area_of_rectangle"
,al endprogram area_calculation
module rec publicarea contains function
area(a,b)result (al) real, intent(in)a,b reala
l alab return endfunction area end module rec
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• Write a program using either subroutine or
  function
• read the three edges of a triangle,
• write a subprogram which calculate area of
  triangle

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program
subprogram
!this program calculate area of a triangle !using
subroutine program triangle_area use ak real
a,b,c,al print ,"a,b,c" read ,a,b,c call
alan(a,b,c,al) print ,al end program
triangle_area
module ak public alan contains subroutine
alan(a,b,c,al) real, intent (in)a,b,c real,
intent (out)al real s s(abc)/2
alsqrt(s(s-a)(s-b)(s-c)) return end
subroutine alan end module ak
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program
subprogram
module ak public alan contains function
alan(a,b,c) result (al) real, intent(in)
a,b,c real al real s s(abc)/2.0
alsqrt(s(s-a)(s-b)(s-c)) return end
function alan end module ak
program triangle_area use ak real
a,b,c,al print ,"a,b,c" read ,a,b,c al
alan(a,b,c) print ,al end program triangle_area
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HOMEWORK 2  Dead Line 28 / 03 / 2001 
PROBLEM Consider a geometrical body which
consists of a steel-cylinder and a cone of lead
having the same radius. Then, prepare a computer
program having the structure described in below

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• The main program will read the input values
  (radius r50cm, height of the cylinder, h1300cm,
  height of the cone h2 150cm, density of steel,
  d1 7.85 t/m3, density of lead d2 11.40 t/m3
  )
• calculate the total volume of the given body
• calculate the total weight of the given body
• finally print,
• the input values
• the volume of the cylinder
• the weight
• the volume of the cone
• the weight of the cone
• the total volume of the given body
• the total weight of the given body
• using list directed output command including the
  above-given expressions for the input values and
  the results obtained.

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A function sub-program will calculate only the
bottom surface area   A subroutine sub-program
will calculate the volume of the cylinder the
weight of the cylinder   Another subroutine
sub-program will calculate the volume of the
cone the weight of the cone