chapter 2:basic elements of fortran programming

7/30/2019 Chapter 2:Basic Elements of Fortran Programming

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Chapter 2

Basic Elements of

Fortran Programming


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Character set (Table 2-1)

26: UPPER CASE A Z

26: lower case a z

10: Digits 0 9

1: Underscore _ 5: Arithmetic symbols + - * / **

17: Other symbols ( ) . = , $ :

! % & ; < > ?

and blank


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Case insensitive

Example: Apple

apple

ApPLe ApplE

Example:

read (*,*) Name

write (*,*) name


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Fortran Statements

Executable statements: Actions taken by program

Examples: Read (*,*) x, y Z = x + y Write (*,*) The result = , z

Nonexecutable statements information for proper operation of program

Examples:

Program name ! This is a comment End program


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Fortran Statements

Each line is 132 characters long

If it does not fit, use & to split a statement Example:

Output = input1 + input2

Output = input1 &

+ input2

Output = input1 &

& + input2

A statement can be split up to 40 lines


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Fortran Statements

Statements can be named using a label

Example: program counter 10 integer :: count = 5 20 write (*,*) count = , count

end program A label should be unique It does not indicate line numbers It can be used more than once

It does not indicate the program sequence/order Not used in modern Fortran 90/95


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Fortran Statements

Comments:

Ignored by Fortran compiler

can appear any where in a line

start with ! to the end of the line Examples:

! This is a counting program

a = b + 1 ! This statement adds one ! Can I put a comment here? a = b + 1


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Fortran Program Structure

Declaration section Programs name

Types of variables and constants

Execution section Actions to be performed by program

Termination section

Stopping (ending) program execution


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Program name

Declaration statements

.Executable statements

..

END Program name


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Example:

program first_program

! This is my first program

integer, parameter :: x = 3, y=4 integer :: z

z = x + y

write (*,*) x + y = , z end program


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Options for Program Termination

end program name end program

end

stop ! to be used in special cases


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Rules of NAMES Any name (program/variable/constant) can be used only once

program counter integer :: counter = 5 write (*,*) counter = , counter end program

Names


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Program styles

A programmer should use a consistent style: Example 1:

PROGRAM example1

REAL :: x, y, z

WRITE (*,*) Enter x, y WRITE (*,*)

READ (*,*) x, y, z

z = x + y

WRITE (*,*) x + y = , z

END PROGRAM


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Program styles

Another programmer can use a different style: Example 2:

program example1

real :: x, y, z

write (*,*) Enter x, y write (*,*)

read (*,*) x, y, z

z = x + y

write (*,*) x + y = , z

end program


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Program styles

This style is not acceptable (but it works!): Example 3:

program example1

real :: x, y, z

WRITE (*,*) Enter x, y write (*,*)

READ (*,*) x, y, z

z = x + y

write (*,*) x + y = , z

end PROGRAM


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Variable vs. Constant

Constant: Once declared, cannot be changed during execution If you try to change it, you get an error Example:

REAL, PARAMETER :: GRADE = 88

GRADE = GRADE / 100 Variable:

Can change value during execution Example

REAL :: GRADE = 88 GRADE = GRADE / 100


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Data dictionary

In the header of the program

Example: program converter

! This program converts US Dollars to Omani Rials.

! We use the variables:

! USD: US Dollars

! OR: Omani Rials

end program


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More about data types

3 Numeric: INTEGER REAL

COMPLEX (not covered)

1 Strings of Characters: CHARACTER

1 Logical: LOGICAL

Others: Chapter 12: derived data types (not covered in this course)


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INTEGER:

Either constant or variable

+ve, -ve, zero

1,000,000 (error: commas not allowed)

-100.

(error: decimal point not allowed)


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REAL: Constants must have a decimal points ( 300.) 10,000,000.

(error: commas not allowed)

105 (error: decimal point missing)

123E5

(error: decimal point missing in mantissa)

-34E2.5 (error: decimal point not allowed in exponents)


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More about data types CHARACTER:

Example1 Character :: name name = Ramadhan Write (*,*) name

Example2

Character (len=8) :: name name = Ramadhan Write (*,*) name

Example3 Character (len=14) :: word1

Character (len=6) :: word2 word1 = Ramadhan Word2 = kareem Write (*,*) word1, word2


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CHARACTER:

Using single/double quotes Example1:

Name = Abdullah Name = Abdullah Name = Abdullah Name = Abdullah Write (*,*) I read quran daily Write (*,*) I read quran daily Write (*,*) I read quran daily

Each one surrounds the other: Solar energy is a clean source of energy Hes wasting time watching useless TV programs


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Implicit none

It checks that variables types are declared Without it:

Any undeclared variable starting with I, J, K, L, M, N areintegers (default typing)

Other variables are real (default typing)

Examples: Program checking read (*,*) monthly_income annual_income = monthly_income * 12 write (*,*) Annual income = , annual_income End program


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Initializing Variables

Three ways to initialize

Initialize at declaration section

Using assignment statement at execution section

Using READ to initialize from input device Non-initialized variables might or might not produce an error. Program might

work in some machines and fail in others or at the same machine might worksome times and fail other times depending on the values stored at thememory location.

Rule: All variables must be initialized before using them.


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Input/output statments READ (*,*)

Standard input device (keyboard) Free input format (decided by variable type) e.g: (try inputting more values for each statement)

READ i READ i, j READ i, j, x, char

(Note: character with specific length will be left justified with all others filled with blankif not entered)

WRITE(*,*) Standard output device (screen) Free output format E.g:

WRITE(*,*) x WRITE(*,*) Result is: , x WRITE(*,*) Result is: , COS(x) WRITE(*,*) Result is: , x, And cosine will be: , cos(x)


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Arithmetic operators Assignment:

Variable_name = expression Example:

Days = months * 30

= is called assignment operator

Binary arithmetic operators (e.g. a + b): + Addition - Subtraction * Multiplication / Division

** Exponentiation Unary arithmetic operators (e.g. b)

+ 34 - a


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Rules No two operators may occur side by side

A * - b A ** -2 A ** (-2)

Implied multiplication is illegal x ( y + z ) x * ( y + z )

Use parentheses to group terms 2 ** ((8+2)/5)


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Real Arithmetic (const. & var.) 3. / 4. = 0.75

4. / 4. = 1. 5. / 4. = 1.25 6. / 4. = 1.5

7. / 4. = 1.75 8. / 4. = 2. 9. / 4. = 2.25

1. / 3. = 0.3333333


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Integer Arithmetic (const. & var.) 3 / 4 = 0

4 / 4 = 1 5 / 4 = 1 6 / 4 = 1

7 / 4 = 1 8 / 4 = 2 9 / 4 = 2

Truncation of fractions


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Be careful..

3. * (1. / 3.) 1. 3. * (0.3333333) = 0.9999999 2. * (1. / 2.) = 1. 2. * (0.5) = 1.


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Evaluating expressions

Example: Distance = 0.5 * accel * time **2 Distance = (0.5 * accel * time) **2

Rules:Parentheses first ( innermost)

2 * ( 3 + ( 4 2 ) 2 )Exponentials (right to left)

2 **2 **3 = 2 **8 = 256Multiplication & Division (left to right)

2 * 4 / 6Additions & Subtractions (left to right)

2 + 6 - 12


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Evaluating expressions Exercise:

Power = (2 6) + ( 2 1 * (5+5) **2 **0) 8 = (2 6) + ( 2 1 * (10) **2 **0) 8 = (2 6) + ( 2 1 * (10) **1) 8

= (2 6) + ( 2 1 * 10) 8 = (2 6) + ( 2 10) 8 = 4 + ( 8) 8

= 4 8 8 = 20 Note: parentheses must be balanced.


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Mixed-Mode expressions

1 + 1 /4 = 1

1. + 1 / 4 = 1.

1 + 1. / 4 = 1.25

Rule: An integer is automatically converted into real in case of

mixed arithmetic


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Mixed-Mode expressions

1 + 1 /4 = 1

1. + 1 / 4 = 1.

1 + 1. / 4 = 1.25

Rule: An integer is automatically converted into real in case of mixed arithmetic Raising a negative number to real power is not possible

2 ** 2 = 4 -2 ** 2 = 4

4 ** 0.5 = 2 -2 ** 0.5 ??


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Data conversion To convert real to integer, use INT

Anything after the decimal point is truncated Example: INT(3.3) = 3 INT(3.) = 3 INT(0.3) = 0

To convert integer to real, use REAL A decimal point is added Example: REAL(3) = 3.

Be careful: NINT INT NINT is used to round to the nearest integer Example: NINT(3.2) = 3 NINT(3.5) = 4 INT(3.5) = 3


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INTRINSIC FUNCTIONS Functions:

Generic functions (accept more than one type of inputs) Specific functions (accept one data type only)

Examples: SQRT(X) ABS(X) SIN(X), COS(X), TAN(X) [X in radian] ASIN(X), ACOS(X), ATAN(X) [result in radian] EXP(X) LOG(X), LOG10(X) MAX(A,B), MIN(A,B)

MOD (A,B)

More (Table 2-4)


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More Examples

y = SIN (theta)y = SIN(theta*(3.141593/180.) ! theta is in degreesREAL, PARAMETER :: deg_2_rad = 3.141593/180.! a constant to convert from !degrees to radian

y = SIN (theta*deg_2_rad)y =SIN(2.57)y = SIN (x)y = SIN(pi*x)

y = SIN(SQRT(x))


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Debugging Fortran Program Errors (bugs)

Eliminating error (debugging)

Types of errors: Syntax errors

Run-time errors

Logical errors

Good practice: Use IMPLICIT NONE

Echo all inputs

Initialize all variables

Use parentheses properly If statement is very long break it into multiple lines

Make sure all function and variables in same units


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Example 2-3

Design a Fortran program that

reads an input temperature in

degrees Fahrenheit, converts it

to an absolute temperature in

kelvins, and writes out the result.


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Example 2-3 SolutionThe relationship between temperature in degrees

Fahrenheit (F) and temperature in kelvins (K) canbe found in any physics textbook. It is


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Example 2-3 SolutionOur program must perform the following steps:

1. Prompt the user to enter an inputtemperature in F.

2. Read the input temperature.

3. Calculate the temperature in kelvins from

previous conversion equation.

4. Write out the result, and stop.

Example 2 3 Program (cont )


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Example 2-3 Program (cont.)

Example 2-4 Background


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Example 2-4 Background

From simple circuit theory, the rms current /,

the real power P, reactive power Q, apparent

power S, and power factor PF supplied to theload are given by the equations

Example 2-4


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Example 2-4

Given the rms voltage of the powersource Vand the magnitude and

angle of the impedance Z, write aprogram that calculates the rms

current I, the real power P, reactivepower Q, apparent power S, and

power factorPF

of the load.


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Example 2-4 Solution

Example 2-4 Program


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Example 2-4 Program

Example 2 4 Program (cont )


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Example 2-4 Program (cont.)

chapter 2:basic elements of fortran programming

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