Please check the website below for lecture notes, HWs and project assignments,

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• Please check the website below for lecture notes,
  HWs and project assignments,
• http//mimoza.marmara.edu.tr/byilmaz

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FORTRAN - Lecture 2

• Data types and Operations

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Data Representation

• Bits (0 and 1)
• Bytes (8 bits)
• Words (more than 1 byte)

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Data types

• numeric data types
• real and integer types
• complex type
• non-numeric data types
• character type
• logical type

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Data types

• integer number
• whole number which has no decimal point
• (fixed point representation)
• examples
• 1
• -24
• 324
• 0

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Data types

• integer number
• the amount of memory devoted to storing integer
  depends on computer configuration.
• 4 bytes integers are the most common, i.e.,
• The smallest int. -2n-1-1
• The biggest int. 2n-1
• Note Attempts to use an integer larger than the
  largest or smaller than the smallest value result
  in error.

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Data types

• real number
• number with decimal fractions - has a decimal
  point
• (floating point or scientific representation)
• Speed of sound 299 800 000 m/s 2.998 x 108
• examples
• 1.23456 0.123456e1 -0.012 1. 2e-2
• 1234. 1.234e3

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Data types

• real number
• 0.2998 X 109
• mantissa exponent
• The real numbers are stored in a computer in a
  similar way.
• Ex
• 4-byte computer 24 bits (mantissa) - 8
  (exponent)real_num mantissa x 2 exponent
• 24 bits mantissa 223 7 significant decimal
  digits
• 8 bits exponent ranges between 2-128 and 2127
  10-38 to 1038

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Data types

• real number
• Ex 12345678.9 will be stored in 12345680.0
• 1 000 000.0 and 1 000 000.9 is same
• The difference is called ROUNd OFF error.
• Ex Find the the max and minimum values can be
  stored in a 2 byte computer.

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Data types

• complex number
• represented as a pair of real (floating point)
  numbers
• first component represents the real part
• second component represents the imaginary
  part of a complex data
• examples
• (6.94, -5.9) (3.942, 2.5e-3)

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Data types

• character
• sequence of symbols from the Fortran character
  set - enclosed between double or single quotes
• Character data consists of
• 26 uppercase and 26 lowercase letters from A to Z
• 10 digits 0-9
• Common symbols (-_/ etc.
• examples A character 123456
• 1234abc

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Data types

• character
• a character data is stored in 1 byte
• The particular bit values may vary from computer
  to computer depending on the coding system used
  for the characters
• ASCII (Am. Stand. Code for Information
  Interchange)
• EBCDIC
• UNICODE (2 byte)

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Data types

• logical
• has the value
• .TRUE. or .FALSE.

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Program Structure

• Heading
• program, function, subroutine, module
• Specification statements
• implicit-type / explicit-type declarations
• Executable statements
• Internal subprograms
• End statement

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Program Structure

• One Fortran line can contain 132 characters in
  Fortran 90/95, if longer lines are needed
  symbol can be used to divide the line
• Ex output input1 input2
• output input1
• input2
• ! is used for comments, when used the line is
  converted to a non-executable statement

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Example

• program celsius_to_fahrenheit
• ! A program to convert a Celsius temperature to
  Fahrenheit
• ! Variable declarations
• real temp_C, temp_F
• ! Ask for Celsius temperature
• print , What is the Celsius temperature?
• read , temp_C
• ! Convert it to Fahrenheit
• temp_F 9.0temp_C/5.0 32.0
• ! Print both temperatures
• print , temp_C, temp_F
• end program celsius_to_fahrenheit

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Constants and Variables - Names

• A data object is either a constant that never
  changes or a variable that can change during
  program execution.
• A variable occupies storage inside the computer
• A numerical constant, a character constant, or a
  logical constant in a program may have an
  explicit form.
• Alternatively a constant may be represented by a
  name

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Constants and Variables - Names

• Data object names
• a name may contain up to 31 letters (upper case
  or lower case characters), digits and underscore
  characters
• first character must be a letter
• examples
• X
• Kinetic_Energy
• aBc_defG1789

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Type declarations

• form
• type name list of names
• examples
• integer Counts, Flag
• real Speed, Distance, Time
• complex Case
• character First_name, Last_name
• logical control

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Type properties

• form
• type name (type properties) list of names
• kind and length of a data object
• examples
• character (len10) First_name, Last_name

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Type attributes

• form
• type name (type properties), attributes list
  of names
• examples
• integer, parameter ARRAY_SIZE 12, SL 20
• character (lenSL), save Element_Name
• integer, dimension(ARRAY_SIZE) Chart, List
• Element_Name has string length 20
• ARRAY_SIZE and SL have parameter attribute
• Element_Name has save attribute
• Chart and List have dimension attribute
  (dimension is 12)

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Properties

• Properties takes these keywords
• len used for defining the length of characters
• kind defines the properties of integer, real
  and complex variables
• kind (real variables)
• 1 single precission (approx. 7 significant
  digits, usually stored in 32 bits)
• 2 double precission (approx. 14 significant
  digits, usually stored in 64 bits)

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Properties

• kind (integers)
• 1 1 byte integer (range is from -27 to 27 - 1)
• 2 2 byte integer (range is from -215 to 215 -
  1)
• 3 4 byte integer (range is from -231 to 231 -
  1)
• 4 8 byte integer (range is from -263 to 263 - 1)
• constant data types can be assigned by placing
  an underscore followed by the value of its kind
• 1234325424_4
• also means integer number of type 4

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Attributes

• dimension points an array of variable
• parameter states that its value is used as a
  constant
• save saves the variable value - in function or
  subroutine returns to calling program
• allocatable used for dynamic storage of variables
• pointer used for accessing memory locations
• target used for pointing memory for pointers
• public declaration of variable that other
  subprograms or main program can access
• private declaration of variables that no other
  program can use

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Implicit none

• this statement should be placed at the beginning
  of the declarations
• every variable and named constant used in the
  program should then be defined by a type
  declaration

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Initial values for variables

• initially a variable has no value (it is
  undefined)
• initial values can be specified in a type
  declaration
• real a 1.25, b 2.5, c 5.0
• during program execution a variable can be
  defined if it appears on the left side of an
  assignment statement
• Variable name Expression

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Assignment statement

• mass 100.
• Velocity 12.5
• Kinetic_Energy 0.5 mass Velocity 2
• Assignment is not a statement of algebraic
  equality
• I I 1

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Constants

• named constants can be initialized within a
  declaration list
• integer, parameter ARRAY_SIZE 12
• the keyword parameter designates a named
  constant
• explicit constants are given in statements
• it is a good practice to use capital letters for
  all named constants
• ARRAY_SIZE, PI, UNIV_GAS_CONSTANT

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Constants

• Houdini Principle
• do not use magic numbers (other than 0 and 1)
• use a named constant rather than an explicit
  constant
• always explain the constants used by comment
  lines
• (in comment line, the first nonblank character
  is an exclamation mark, !)

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Arithmetic operations

• addition and subtraction
• X 5.0
• J - 4
• A B - C
• multiplication and division
• X 2.0
• A / B
• Old_vol ( Old_pres / New_pres ) ( New_temp /
  Old_temp )
• exponentiation
• A 2.0
• 0.5 Mass Velocity 2

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Operators

• Operator Operation
• addition, (plus ? identity)
• - subtraction, (minus ? negation)
• multiplication
• / division
• exponentiation
• two operators must not appear side by side in an
  expression
• A ( - B )

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Importance of numerical data types

• When all operands are real, the result type is
  real - when all operands are integers, the result
  type is integer
• in integer division, the result is truncated to
  the next smaller integer
• 9 / 5 ? 1
• 9.0 / 5.0 ? 1.8
• when a real expression is raised to an integer
  power, the result type is real
• A 5 ? AAAAA ? A 5.0 less efficient

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Arithmetic operations

• examples
• to calculate F ( 9 C / 5 ) 32
• F 9.0 C / 5.0 32.0
• to calculate a b2 c2
• A B2 C2

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Arithmetic operator priorities

• Operator Priority
• low
• - low
• medium
• / medium
• high

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Priorities

• Subexpressions enclosed in parentheses are
  computed first - innermost parenthesized
  subexpression is evaluated first
• ( 5.0 3.0 ) / 2.0 ? 4.0
• arithmetic operations are performed according to
  the operator priorities
• 5.0 3.0 / 2.0 ? 6.5

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Priorities

• operations are performed in order from left to
  right - however two or more consecutive
  exponentiation operations are performed in order
  from right to left
• 5.0 3.0 / 2.0 ? 7.5
• 5.0 3.0 2.0 ? 59
• function evaluation takes precedence over all
  other operations
• abs ( A ) B / C
• sqrt ( 4.0 ) 3.0 / 2.0 ? 3.0

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Logical Calculations

• Form
• logical var. name logical expression
• Relational Oper.s Combinational Oper.s
• equal .AND.
• / not equal .OR.
• gt Greater than .EQ.
• gt greater equal .NOT.
• lt less than
• lt less and equal
• Note staments are executed from left to right

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Cahracter Variables

• Character (len3)ff1, ff2
• ff1f ! ff1 f
• ff2file01 ! ff2 fil
• Concatenation Operator (//) combines two or more
  strings into a single large string,
• Ex character(len10)a
• character(len8)b,c
• aABCDEFGHIJ
• b12345678
• ca(13)//b(45)//a(68)
• cABC45FGH

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Functions

• type conversion functions
• X real ( I 3 ) / 3.0
• J int ( X ) I
• numerical utility functions
• abs (X) absolute value
• max (X, 0.0, Z) produces largest argument value
• min (J, K) produces smallest argument value
• sign (1.0, X) transfers sign of 1st argument
  to the 2nd
• modulo (K, J) gives remainder from division

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Functions

• mathematical functions
• acos inverse cosine
• asin inverse sine
• atan inverse tangent
• atan2 inverse tangent
• cos cosine
• cosh hyperbolic cosine
• exp exponential
• log natural logarithm
• log10 common logarithm

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Functions

• mathematical functions (continued)
• sin sine
• sinh hyperbolic sine
• sqrt square root
• tan tangent
• tanh hyperbolic tangent

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Input and output

• read statements
• read , input-list
• read (unit ,fmt ) input-list
• write statements
• print , output-list
• write (unit , fmt ) output-list

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Example

• problem
• write a program to read a Celsius temperature
  and convert it to Fahrenheit using the formula,
• F ( 9 C / 5 ) 32
• analysis
• write down a structure plan first
• read Celsius temperature (temp_C)
• convert to Fahrenheit (temp_F)
• print both temperatures

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Example

• solution
• program celsius_to_fahrenheit
• ! A program to convert a Celsius temperature to
  Fahrenheit
• ! Variable declarations
• real temp_C, temp_F
• ! Ask for Celsius temperature
• print , What is the Celsius temperature?
• read , temp_C
• ! Convert it to Fahrenheit
• temp_F 9.0temp_C/5.0 32.0
• ! Print both temperatures
• print , temp_C, temp_F
• end program celsius_to_fahrenheit