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FORTRAN 90 Lecture : Rafel Hekmat Hameed University of Babylon Subject : Fortran 90 College of Engineering Year : Second B.Sc Mechanical Engineering Dep. 1.DATA TYPE 1.1 CONSTANT Fortran has six types of constants: integer, real, complex, logical, double precision, and character string. Integer Constants: a string of digits with an optional sign: Examples: 0, -345, 768, +12345 Real Constants: There are two representations, decimal representation and exponential representation. o Decimal Representation: A decimal point must be presented, but no commas are allowed. A real constant can have an optional sign. Examples: 23.45, .123, 123., -0.12, -.12 o Exponential Representation: It consists of an integer or a real number in decimal representation . Examples: 12.3458E2 or 12.3458e2: this is equal to 1234.58 -3.14E1 or -3.14e1: this is equal to -31.4 -1.2E-3 or -1.2e-3: this is equal to -0.0012 12E3 or 12e3: this is equal to 12000.0 0E0 or 0e0: this is equal to 0.0 ϭ Complex : Two real number stored as a pair and treated as the real and imaginary parts of a complex number. Examples: (1.234,-6.5E-3) Where in this example, 1.234 is the real part of the complex constant and -0.0065 is the imaginary component. Examples: complex:: x,y,i x=(1,1) y=(1,-1) i=(0,-1) print*,conjg (x),i*x*y end Logical : Logical variables have a value of either .true. or .false. Character String: Character constants must be enclosed between double quotes or apostrophes (single quotes). The content of a string consists of all characters, spaces included, between the single or quote quotes, while the length of the string is the number of characters of its content. The content of a string can be zero and in this case it is an empty string Examples: 'Ali' and "Ali": content = Ali and length = 3 ' ' and " ": content = a single space and length = 1 'ahmed #2' and "ahmed #2": content = ahmed #2 and length = 8 '' and "": content = nothing and length = 0 (empty string) Double precision : are similar to real number but are allocated twice as much storage space. and can lie in approximate range 10-307 to 10308. Ϯ 2. Fortran Variables and Their Types A Fortran variable can be considered as a box that is capable of holding a single value of certain type. Thus, a variable has a name, the variable name and a type. The type of a variable can be one of the following: INTEGER: the variable is capable of holding an integer REAL: the variable is capable of holding a real number COMPLEX: the variable is capable of holding a complex number LOGICAL: the variable is capable of holding a logical value (i.e., true or false) CHARACTER: the variable is capable of holding a character string of certain length 2.1 Fortran Variable Declarations Declaring the type of a Fortran variable is done with type statements. It has the following form: type-specifier :: list where the type-specifier is one of the following and list is a list of variable names separated with commas: INTEGER : the variables in list can hold integers REAL: the variables in list can hold real numbers COMPLEX: the variables in list can hold complex numbers LOGICAL: the variables in list can hold logical values (i.e., true or false) CHARACTER: the variables in list can hold character strings Types INTEGER and REAL . Examples: Variables ZIP, Mean and Total are of type INTEGER: INTEGER :: ZIP, Mean, Total INTEGER :: a = 828, b = 59 Variables Average, error, sum and ARAE are of type REAL: ϯ REAL :: Average, error, sum, AREA REAL :: a = 2.61828, b = 3.14159 Type CHARACTER is more involved. Since a string has a length attribute, a length value must be attached to character variable declarations. There are two ways to do this: Use CHARACTER(LEN=i) to declare character variables of length i. For examples, Name and Street are character variables that can hold a string of no more than 15 characters: CHARACTER(LEN=15) :: Name, Street Use CHARACTER(i) to declare character variables of length i. That is, there is no LEN= in the parenthesis. For examples, Name and Street are character variables that can hold a string of no more than 15 characters: CHARACTER(15) :: Name, Street If a variable can only hold a single character, the length part can be removed. The following three declarations are all equivalent: CHARACTER(LEN=1) :: letter, digit CHARACTER(1) :: letter, digit CHARACTER :: letter, digit Here, variables letter and digit can only hold no more than one character. If the length value is replaced with a asterisk *, it means the lengths of the declared variables are determined elsewhere. CHARACTER(LEN=*) :: Title, Position Here, the actual lengths of variables Title and Position are unknown and will be determined elsewhere. ϰ 3. PARAMETERS It refers to a value which will not change during a program’s execution. REAL, PARAMETER :: pi=3.141592 INTEGER, PARAMETER :: maxvalue=1024 CHARACTER(LEN=4), PARAMETER :: Name = 'Smith' It is an error to try to redefine the value of a parameters while a program executes. 4. Implicit Declaration Fortran 90 permits real and integer variables to be typed and declared implicitly, that is used in a program without using a declaration statement. It is possible and advisable, to disable this feature by including the statement: IMPLICIT NONE at the start of each program. This forces a programmer to declare all variables that are used, and means that some potential errors may be identified during compilation. If implicit typing is permitted then variables are have a data type according to the initial letter of their name: those beginning with I, J, K, L, M and N being integers; and those beginning A to H and O to Z being real. PROGRAM free_source_form IMPLICIT NONE REAL :: tx, ty, tz tx = 1.0; ty = 2.0; tz = tx * ty ! Continuation symbol on line to be continued PRINT *, & tx, ty, tz END PROGRAM free_source_form ϱ