البرنامج صياغة Coding the Program

التدفق Flowchart خرائطخرائط أيضا� عليها ويطلق

مجموعة وهي العمليات سيرعليها المتعارف الرموز منالخطوات لتوضيح تستخدم

مشكلة لحل الالزمة المنطقية.ما

البرنامج عناصر

1. Program name

2. Type declarations

3. Assignment and 4. Input/Output Statements

5. Comments

6. Subprograms

program Hello! ! talk to the computer! write (*,*) 'Hello, world' stop end

Hello1

Fortran 90: Data types and constants

CHARACTER constant: a string of one or more characters between single or double quotes. e.g. "Fred", ' ' (a blank)

Numerical constants may be positive, negative or zero. If positive the sign is optional.

Embedded commas (e.g. 1,000,000) or spaces (1 000 000) are not permitted.

INTEGER constant: any number not containing a decimal point and/or exponent. e.g. 2153 -36 0 123456 999 Range is machine dependent. On SUN, PC and many others to > |2 000 000 000| Complete accuracy. (32 bits = 4 bytes)

REAL constant: any number containing a decimal point and/or exponent (“scientific” notation) e.g. 21.362 -9.6405 0.0 -25. .00125 The exponent is the letter E followed by an integer constant representing a power of 10

e.g. -3.5E4 ( 3 5 .(

104 ) 0.263E-6 0 263 10 6

. )

5E+12 ( 5 1012) 1E-8 ( 10 8 )

decimal point not required if exponent present. Precision depends on computer and compiler. SUN, PC: 6 to 7 decimal digits Exponent range is ±38 ~ ± ± 10 38

REAL numbers: Beware of rounding errors and truncation.

DOUBLE PRECISION: for greater range and precision (64 bits total). 15-17 digits, range . Constants must be in exponent form using D.

~ ± ±

10 308

e.g. 5D12, 3.141592653589793D0, 1D0 STRONGLY RECOMMENDED FOR SCIENTIFIC WORK

Fortran 90: Standard character set

A to Z (upper case), digits 0 to 9, underscore _ special characters: space = + - * ( ) , . ' : " !

% & ; < > ? $ For portability it is advisable to stick to these characters even in character constants, but most computers now use the ASCII character set to represent characters as 8 bit numbers (0-255). additional characters: a to z (lower case), # @ [ \ ] ^ ` { | } Any character acceptable to the computer may be used in CHARACTER constants.

WARNING: Fortran compilers do not distinguish between upper

and lower case except in character constants. i.e. ABCDE abcde AbCdE aBcDe, etc.

Other data types: LOGICAL, COMPLEX

Variable names: (and most other names, e.g. for PROGRAM) First character must be a letter.Remaining characters may be any combination of letters, digits or underscore ( _ ) characters. Maximum length is 31 characters. e.g. A A12 Alpha_3 Next_Month width

Variables are names of ‘boxes’ in computer memory where numerical or other data values are stored.

We must tell the compiler what type of data they will hold by declaring all variables in Type statements. e.g. old style new style

REAL a, b, c or REAL :: a, b, c INTEGER count, year INTEGER :: count,

year Use IMPLICIT NONE at the start of each program

unit.

Use comments to create a variable dictionary.

Hello 2

program Hello! implicit none real first, second, average! ! talk to the computer! write (*,*) 'Hello, world' read (*,*) first read (*,*) second average = (first+second)*0.5 write (*,*) average stop end

Hello 3program Hello! implicit none real first, second, average! ! talk to the computer! write (6,*) 'Hello, world' read (5,*) first read (5,*) second average = (first+second)*0.5 write (6,*) average stop end

Hello 4program Hello!! with good programming habits! implicit none real first, second, average integer kread, kwrite data kread/5/, kwrite/6/! ! talk to the computer! write (kwrite,*) 'Hello, world' read (kread,*) first write (kwrite,*) 'first variable:', first read (kread,*) second write (kwrite,*) 'second variable:', second average = (first+second)*0.5 write (kwrite,*) 'average of first and second variable is:', average stop end

program mprecision !! check out machine precision! implicit nonereal epssp, onesp double precision epsdp,onedp integer n,i integer kread, kwrite Data kread/5/, kwrite/6/ !epssp=1. epsdp=1.d0 !single precision: do n=1,20 do i=1,10 epssp=epssp/2. onesp= 1. +epssp end do write (kwrite,*) 'loop number',n*10,' onesp =',onesp,' epssp =', & & epssp end do write (kwrite,*) write (kwrite,*) ! double precision: do n=1,40 i=1,10 epsdp=epsdp/2.d0 onedp= 1. +epsdp end do write (kwrite,*) 'loop number',n*10,' onedp =',onedp,' epsdp =', & & epsdp end do stop end