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Example in Final Fall 2006

PROGRAM EXAM IMPLICIT NONE INTEGER :: A=3, B=8 REAL :: CALC B = CALC (A, B) A = CALC(A, B) WRITE(*,*) A, B END PROGRAM EXAM a) 0 0 b) 3 0 c) 0 3 d) 0 8 e) None of the above. REAL FUNCTION CALC(X, Y) IMPLICIT NONE INTEGER :: X, Y IF(X > Y) THEN Y = Y/X CALC = Y  ELSE

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Example in Final Fall 2006

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  1. PROGRAM EXAM IMPLICIT NONE INTEGER :: A=3, B=8 REAL :: CALC B = CALC(A, B) A = CALC(A, B) WRITE(*,*) A, B END PROGRAM EXAM a) 0 0 b) 3 0 c) 0 3 d) 0 8 e) None of the above REAL FUNCTION CALC(X, Y) IMPLICIT NONE INTEGER :: X, Y IF(X > Y) THEN Y = Y/X CALC = Y  ELSE CALC = Y/X END IF END FUNCTION CALC Example in Final Fall 2006

  2. PROGRAM midterm IMPLICIT NONE INTEGER :: a, b a = 15 b = 5 CALL mysub(a, b) WRITE(*,*) b-a END PROGRAM a). -6532 b). -150 c). 1 d). 2356 e). None of the above SUBROUTINE mysub(b,a) IMPLICIT NONE INTEGER a, b, i, j IF(a > b) THEN a = (a - 10)**2 b = b*b ELSE a = a*b b = b*b END IF if(a == b) THEN DO i=1, 15 DO j=i, 25-i a = a + i*j b = b - a END DO END DO IF(a /= b) THEN a = 2 b = 3 END IF END IF END SUBROUTINE Example in Midterm Fall 2006

  3. Formatting input and output Yi Lin

  4. Output: 1.100000 1100.100 Nicer format: 1.1000 1100.1003 Why formatting? PROGRAM test IMPLICIT NONE REAL::x=1.1, y=1100.1003 WRITE(*,*) x WRITE(*,*) y END PROGRAM

  5. FORMAT statement • Syntax write(*, label) list-of-variables labelformatformat-code • Semantics • Output list-of-variables according to the format-codes specified on the line labeled.

  6. label format-code FORMAT statement, example 1 • Example REAL::y=1100.1003 write(*, 900) y 900 format (F10.4) • F10.4 means that the number y should be printed using fixed point notation with field width 10 and 4 decimal places. #1100.1003 Width=10 (including “.”, white spaces will be filled on the leftmost side) Decimal digits=4

  7. List-of-variables FORMAT statement, example 2 • Example REAL::x=1.0, y=1100.1003 write(*, 900) x, y 900 format (F3.1, F10.4) • F3.1 is for x and F10.4 is for y correspondingly. 1.0#1100.1003 (#: white space) • Width should be larger enough!

  8. FORMAT statement, example 4 • Example REAL::x=1.0, y=1100.1003 write(*, 900) x, y 900 format (F3.1, F9.4) • (F3.1,F9.4): 1.01100.1003 • (F3.1,F10.4): 1.0#1100.1003 • (F3.1,F8.4): 1.0******** • *: Width=8 is not wide enough to output y. • 4 integer digits + 4 decimal digits + 1 for “.” = 9 digits

  9. Common format codes • E.g., 900 format (F10.4) • The most common format code letters are: F - real numbers, fixed point format I - integer A - text string E - real numbers, exponent notation X - horizontal skip (space) / - vertical skip (newline)

  10. d=4 #1100.1003 w=10 (including “.”) FORMAT statement, Fw.d • The format code F (and similarly D, E) has the general form Fw.d where w is an integer constant denoting the field width and d is an integer constant denoting the number of decimal digits. F10.4 • If a number or string does not fill up the entire field width, spaces will be added. Usually the text will be adjusted to the right, but the exact rules vary among the different format codes.

  11. FORMAT statement, Exponent notation • E: Exponent notation REAL::y=1100.1003 WRITE(*,100) y 100 FORMAT(E10.2) d=2 ##0.11E+04 w=10 (including “.”)

  12. A5 I6 ###a=##1000 A I4 a=1000 A I3 a=*** FORMAT statement, example 5 • For integers only the field width is specified, so the syntax is Iw. Similarly, character strings can be specified as Aw but the field width is often dropped. INTEGER::a=1000 WRITE(*,100) “a=“, a 100 FORMAT(A5,I6) WRITE(*,200) “a=“,a • FORMAT(A,I4) WRITE(*,300) “a=“,a 300 FORMAT(A,I3)

  13. A 4X I4 a=####1000 A X I4 a=#1000 FORMAT statement, horizontal skip • nX: horizontally skip n spaces INTEGER::a=1000 WRITE(*,100) “a=“, a 100 FORMAT(A, 4X, I4) • If n is omitted, n=1 100 FORMAT(A,X,I4)

  14. A a= # # 1000 2/ I4 FORMAT statement, vertical skip • n/: vertically skip n lines INTEGER::a=1000 WRITE(*,100) “a=“, a 100 FORMAT(A, 2/, I4) • If n is omitted, n=1

  15. I4 I4 I4 ###1##10#100 FORMAT statement, repeating • nIw: = repeat Iw n times INEGER::a=1, b=10, c=100 WRITE(*,100) a,b,c 100 FORMAT(3I4) • And similarly nFw.d

  16. FORMAT statement, repeating (cont.) • n(format-codes): = repeat format-codes n times FORMAT(3(I4,F10.4)) Is equivalent to FORMAT(I4,F10.4,I4,F10.4,I4,F10.4)

  17. FORMAT statement, Simplified form • Format strings in read/write statements write (*,”(A, F8.3)”) “The answer is x = “, x • is equivalent to write (*,990) “The answer is x = “, x 990 format (A, F8.3) • Sometimes text strings are given in the format statements, e.g. the following version is also equivalent: write (*,999) x 999 format (“The answer is x = “, F8.3)

  18. FORMAT statement, READ • All of these format-codes are also applied to READ statement. INTEGER::a,b READ(*,*) a,b • From the keyboard, we just need to type 1,2 (or 1#2) ! a=1, b=2 • But with formatting input, we must be careful about the number of spaces input.

  19. FORMAT statement, READ • Example INTEGER::a,b READ(*,100) a,b • FORMAT(2I3) ! eqv. To FORMAT(I3,I3) • If inputting “1,2”, the computer will take the first 3 characters “1,2” and assign them to a. Runtime error! “1,2” not an integer • If input “##1, 2”, a=##1. But “,2###” will be assigned to b. Runtime error!

  20. FORMAT statement, READ • Correct inputs for (2I3), e.g., • “##1##2” a=##1, b=##2 • “1##2##” a=1##, b=2## • “#1##2#” a=#1#, b=#2# • What if “#1#22222”? • a=#1#, b=222

  21. FORMAT statement, READ • Correct inputs for READ(*, “(F5.1)”) x? • “##3.4”  x=3.4 • “123.456”  x=123.4 • “12345”  x=1234.5 (take the leftmost 5 digits first, then assign the last digit as decimal part and the leftmost 4 digits as integer part)

  22. Format Read • Example INTEGER::a, b,c READ(*,100) a,b,c • FORMAT(I3,x,I2,2x,I4) • Input: 123456789 • A=123 • B=56 • C=9

  23. File input/output • READ(*,*)/WRITE(*,*) only reads from/writes to standard input(e.g., keyboard)/output(screen). • Files: a data storage unit in hard disks. • E.g., HelloWorld.f90 • E.g., studentRecords.txt • E.g., experimentalData.txt • We need to read data from existing files and/or write data to files.

  24. File input/output • Three steps to use a file • Open a file • Input/output using READ and WRITE • READ: read data from the opened file • WRITE: write data to the opened file • Close the file (A file that has not been closed can usually not be read. )

  25. File input/output, OPEN • To open a file, syntax: OPEN ([olist] ) • where, olist is a list of keyword clauses separated by “,”: keyword "=" value {"," keyword "=" value} • Example: OPEN(UNIT=10, FILE=“expData.txt”)

  26. File input/output, OPEN • Important keywords: [UNIT=] u ! u is a unique number to identify the file FILE= fname ! File name • Some other keywords (not required in course materials) STATUS, ERR, ISOTAT, ACCESS, FORM, RECL, POSITION

  27. File input/output, OPEN • [UNIT=]u • OPEN(10, “expData.txt”) • OPEN(UNIT=10, “expData.txt”) • Unit number (i.e., u) is an integer from 1-99, with some reserved: • 5: standard input • READ(*,*) == READ(5,*) • 6: standard output • WRITE(*,*) == WRITE(6,*)

  28. FILE input/output, READ/WRITE • READ READ(unit, label) list-of-variables label format(format-codes) or READ(unit, *) … • WRITE WRITE(unit, label) list-of-variables label format(format-codes) or WRITE(unit, *) …

  29. FILE input/output, CLOSE • A file that has not been closed can usually not be read. • Syntax: CLOSE ([UNIT=]u) • For example: CLOSE (10) CLOSE (UNIT=10)

  30. a=######51 a=#######6 … inputData.txt FILE input/output, Example ! Input 10 integers from keyboard and write them to file “inputData.txt” PROGRAM fileTest IMPLICIT NONE INTEGER::count, a OPEN(UNIT=10,FILE=“inputData.txt”) ! Open file “inputData.txt” DO count=1,10 WRITE(*,*) “Input an integer number from keyboard:” READ(*,*) a WRITE(10,100) “a=“, a ! Write to “inputData.txt” END DO CLOSE(10); ! Close file “inputData.txt” • FORMAT(A2, I8) END PROGRAM

  31. program mid implicit none integer :: i character*1 :: a(4) read(*,7) (a(i), i = 1,4) 7 format (4(A1,X)) write(*,8) (a(i), i = 4,1,-1) 8 format (4A1) end program There will be an error message because the input string is too long pmoc iumc cmui None of the above. Example in Midterm Fall 2006

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