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Beginning Fortran
Fortran (77) Basics
22 October 2009
Example Code
• Write a program to read in five values of
temperature in Fahrenheit and convert to
degrees Celsius OR Kelvin OR both.
Your Typical Program
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PROGRAM MYPROGRAM
Program Options
Declaration of Variables
MAIN CODE
STOP
END
Your Typical Program
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PROGRAM MYPROGRAM
Program Options
Declaration of Variables
MAIN CODE
STOP
END
Program Declaration
• You declare what kind of Fortran file you are
writing on the first line.
• Syntax: <TYPE> <NAME>
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PROGRAM CONVERTF
Program Declaration
• You declare what kind of Fortran file you are
writing on the first line.
• Syntax: <TYPE> <NAME>
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PROGRAM CONVERTF
Specifies the file as a program
Program name – something short but descriptive
Your Typical Program
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PROGRAM CONVERTF
Program Options
Declaration of Variables
MAIN CODE
STOP
END
Options and Variables
• There are numerous options – you can Google
them if you are interested
• In general, there are two kinds:
– You can “include” variables from another *.h file
by putting include ‘<filename>.h’in the
options section.
– You can switch on other options about how the
code is run (Google it)
– We are going to use implicit none
Options and Variables
• All variables we are going to use must be
accounted for in the declaration section (no
implicit variables allowed) – implicit
none
• What do we need?
– Temperature in Fahrenheit, Celsius, Kelvin
– Logicals (do we want Celsius, Kelvin, both?)
– Some integer to loop through all 5 values
– Syntax: <TYPE> <NAME>
Options and Variables
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IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT)
REAL K(NT)
REAL C(NT)
LOGICAL DOC
LOGICAL DOK
INTEGER I
Options and Variables
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IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT) Specify a special parameter – an
unchangeable value that can
be used (unlike a
REAL K(NT) immediately
variable, which can change value)
REAL C(NT)
LOGICAL DOC
LOGICAL DOK
INTEGER I
Options and Variables
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IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT) Array of 5 REALs for Fahrenheit temps
REAL K(NT)
REAL C(NT)
LOGICAL DOC
LOGICAL DOK
INTEGER I
Options and Variables
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IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT)
REAL K(NT) Array of 5 REALs for Kelvin temps
REAL C(NT)
LOGICAL DOC
LOGICAL DOK
INTEGER I
Options and Variables
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IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT)
REAL K(NT)
REAL C(NT) Array of 5 REALs for Celsius temps
LOGICAL DOC
LOGICAL DOK
INTEGER I
Options and Variables
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IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT)
REAL K(NT)
REAL C(NT)
Do we want to convert to Celsius
LOGICAL DOC Logical:
(TRUE) or not (FALSE)?
LOGICAL DOK
INTEGER I
Options and Variables
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IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT)
REAL K(NT)
REAL C(NT)
LOGICAL DOC
Do we want to convert to Kelvin
LOGICAL DOK Logical:
(TRUE) or not (FALSE)?
INTEGER I
Options and Variables
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IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT)
REAL K(NT)
REAL C(NT)
LOGICAL DOC
LOGICAL DOK
Integer that counts from 1 to 5 for loop
INTEGER I over one-dimensional arrays
Your Typical Program
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PROGRAM CONVERTF
IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT)
REAL K(NT)
REAL C(NT)
LOGICAL DOC
LOGICAL DOK
INTEGER I
MAIN CODE
STOP
END
Main Code
• We need to do several things:
– Read in 5 values of temperature
– Determine if we need to convert to Celsius, Kelvin,
or both
– Output values
Ki
From User
To User
DOK
F
Fi
Ci
DOC
To User
To User
Read in 5 values of F
into array
Ki
From User
To User
DOK
F
Fi
Ci
DOC
To User
To User
For each of the five
temperatures (for-loop):
Ki
From User
To User
DOK
F
Fi
Ci
DOC
To User
To User
Compute C (we are going to do this no matter
what, because we know that the output has to
either be C or K or both, and we need C in
order to calculate K anyway).
Ki
From User
To User
DOK
F
Fi
Ci
DOC
To User
To User
Output F to user (this
should be done just to
make sure that the
input was read
correctly).
Ki
From User
To User
DOK
F
Fi
Ci
DOC
To User
To User
If DOC = TRUE, then
output C as well.
Ki
From User
To User
DOK
F
Fi
Ci
DOC
To User
To User
If DOK = TRUE, then
compute K from C and
output to user as well.
Ki
From User
To User
DOK
F
Fi
Ci
DOC
To User
To User
From User
Main Code
F
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DO I = 1, NT
READ(*,*) F(I)
ENDDO
From User
Main Code
F
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DO I = 1, NT
READ(*,*) F(I)
ENDDO
READ is a Fortran command that is used for input.
Syntax: READ(<location>,<formatting>)
Location (*) = read in from the terminal
Format (*) = no particular format
From User
Main Code
F
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DO I = 1, NT
READ(*,*) F(I)
ENDDO
WRITE(*,*) ‘Convert to C?’
READ(*,*) DOC
WRITE(*,*) ‘Convert to K?’
READ(*,*) DOK
From User
Main Code
F
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DO I = 1, NT
READ(*,*) F(I)
ENDDO
WRITE(*,*) ‘Convert to C?’
READ(*,*) DOC
WRITE(*,*) ‘Convert to K?’
READ(*,*) DOK
Write to screen with no particular formatting.
Main Code
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DO I = 1, NT
C(I) = (5./9.)*(F(I)-32.)
ENDDO
Main Code
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DO I = 1, NT
C(I) = (5./9.)*(F(I)-32.)
ENDDO
For each temperature:
Main Code
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DO I = 1, NT
C(I) = (5./9.)*(F(I)-32.)
ENDDO
For each temperature:
Compute Celsius temp.
Main Code
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IF (DOK .EQV. .TRUE.) THEN
DO I = 1, NT
K(I) = C(I) + 273.15
ENDDO
ENDIF
Main Code
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IF (DOK .EQV. .TRUE.) THEN
DO I = 1, NT
K(I) = C(I) + 273.15
ENDDO
ENDIF
Logical trap: If we want to calculate Kelvin:
Main Code
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IF (DOK .EQV. .TRUE.) THEN
DO I = 1, NT
K(I) = C(I) + 273.15
ENDDO
ENDIF
Logical trap: If we want to calculate Kelvin:
Loop through temperatures and calculate Kelvin temps.
(If DOK = .FALSE., this entire loop is avoided)
Main Code
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IF ((DOC .EQV.
DO I = 1, NT
WRITE(*,*)
ENDDO
ENDIF
c
IF ((DOC .EQV.
DO I = 1, NT
WRITE(*,*)
ENDDO
ENDIF
c
IF ((DOC .EQV.
DO I = 1, NT
WRITE(*,*)
ENDDO
ENDIF
.TRUE.) .AND. (DOK .EQV. .FALSE.)) THEN
F(I), ‘F = ‘, C(I), ‘C’
.FALSE.) .AND. (DOK .EQV. .TRUE.)) THEN
F(I), ‘F = ‘, K(I), ‘K’
.TRUE.) .AND. (DOK .EQV. .TRUE.)) THEN
F(I), ‘F = ‘, C(I), ‘C ’, K(I), ‘K’
Main Code
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IF ((DOC .EQV.
DO I = 1, NT
WRITE(*,*)
ENDDO
ENDIF
c
IF ((DOC .EQV.
DO I = 1, NT
WRITE(*,*)
ENDDO
ENDIF
c
IF ((DOC .EQV.
DO I = 1, NT
WRITE(*,*)
ENDDO
ENDIF
.TRUE.) .AND. (DOK .EQV. .FALSE.)) THEN
F(I), ‘F = ‘, C(I), ‘C’
.FALSE.) .AND. (DOK .EQV. .TRUE.)) THEN
F(I), ‘F = ‘, K(I), ‘K’
.TRUE.) .AND. (DOK .EQV. .TRUE.)) THEN
F(I), ‘F = ‘, C(I), ‘C ’, K(I), ‘K’
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PROGRAM CONVERTF
IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT)
REAL K(NT)
REAL C(NT)
LOGICAL DOC
LOGICAL DOK
INTEGER I
DO I = 1, NT
READ(*,*) F(I)
ENDDO
WRITE(*,*) ‘Convert to C?’
READ(*,*) DOC
WRITE(*,*) ‘Convert to K?’
READ(*,*) DOK
DO I = 1, NT
C(I) = (5./9.)*(F(I)-32.)
ENDDO
IF (DOK .EQV. .TRUE.) THEN
DO I = 1, NT
K(I) = C(I) + 273.15
ENDDO
ENDIF
IF ((DOC .EQV. .TRUE.) .AND. (DOK .EQV. .FALSE.)) THEN
DO I = 1, NT
WRITE(*,*) F(I), ‘F = ‘, C(I), ‘C’
ENDDO
ENDIF
c
IF ((DOC .EQV. .FALSE.) .AND. (DOK .EQV. .TRUE.)) THEN
DO I = 1, NT
WRITE(*,*) F(I), ‘F = ‘, K(I), ‘K’
ENDDO
ENDIF
c
IF ((DOC .EQV. .TRUE.) .AND. (DOK .EQV. .TRUE.)) THEN
DO I = 1, NT
WRITE(*,*) F(I), ‘F = ‘, C(I), ‘C ’, K(I), ‘K’
ENDDO
ENDIF
STOP
END
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PROGRAM CONVERTF
IMPLICIT NONE
PARAMETER NT = 5
REAL F(NT)
REAL K(NT)
REAL C(NT)
LOGICAL DOC
LOGICAL DOK
INTEGER I
DO I = 1, NT
READ(*,*) F(I)
ENDDO
WRITE(*,*) ‘Convert to C?’
READ(*,*) DOC
WRITE(*,*) ‘Convert to K?’
READ(*,*) DOK
DO I = 1, NT
C(I) = (5./9.)*(F(I)-32.)
ENDDO
IF (DOK .EQV. .TRUE.) THEN
DO I = 1, NT
K(I) = C(I) + 273.15
ENDDO
ENDIF
IF ((DOC .EQV. .TRUE.) .AND. (DOK .EQV. .FALSE.)) THEN
DO I = 1, NT
WRITE(*,*) F(I), ‘F = ‘, C(I), ‘C’
ENDDO
ENDIF
c
IF ((DOC .EQV. .FALSE.) .AND. (DOK .EQV. .TRUE.)) THEN
DO I = 1, NT
WRITE(*,*) F(I), ‘F = ‘, K(I), ‘K’
ENDDO
ENDIF
c
IF ((DOC .EQV. .TRUE.) .AND. (DOK .EQV. .TRUE.)) THEN
DO I = 1, NT
WRITE(*,*) F(I), ‘F = ‘, C(I), ‘C ’, K(I), ‘K’
ENDDO
ENDIF
STOP
END
Program Start
Options/Variable Declaration
Main Code
Program End
Compilation
• Compilation is performed in the terminal:
Syntax:
<compiler> -o <exec. filename> <source filename> <options>
Compilation
• Compilation is performed in the terminal:
Syntax:
<compiler> -o <exec. filename> <source filename> <options>
Depends on system: f77, g77, pgf77, etc.
Compilation
• Compilation is performed in the terminal:
Syntax:
<compiler> -o <exec. filename> <source filename> <options>
We wish to create an object that is an executable file with the following name
Compilation
• Compilation is performed in the terminal:
Syntax:
<compiler> -o <exec. filename> <source filename> <options>
Use this *.f file to compile the executable
Compilation
• Compilation is performed in the terminal:
Syntax:
<compiler> -o <exec. filename> <source filename> <options>
Also depends on compiler. Some frequent options:
Mextend – allows you to go over column 70 in the code
Mbounds – if you attempt to reference an array index out of bounds, will notify you
Mbyteswapio – some formats require a byte-swap
Compilation
• Compilation is performed in the terminal:
Syntax:
<compiler> -o <exec. filename> <source filename> <options>
pgf77 –o CONVERTF.exe CONVERTF.f