From edo@wharfrat.as.arizona.edu Mon Aug 27 10:00:36 2001 Received: from wharfrat.as.arizona.edu (wharfrat.as.arizona.edu [128.196.209.89]) by lithops.as.arizona.edu (8.9.1/8.9.1) with ESMTP id KAA02675 for ; Mon, 27 Aug 2001 10:00:36 -0700 (MST) Received: (from edo@localhost) by wharfrat.as.arizona.edu (8.9.1/8.9.1) id KAA27560 for jill; Mon, 27 Aug 2001 10:00:36 -0700 (MST) Date: Mon, 27 Aug 2001 10:00:36 -0700 (MST) From: "E. Olszewski" Message-Id: <200108271700.KAA27560@wharfrat.as.arizona.edu> To: jill@as.arizona.edu Subject: fortran Content-Length: 5756 X-Lines: 198 Status: RO Phys 205, Aug 31 1999 Syntax of FORTRAN programs A cheat sheet for neophytes -------------------------- There are three basic parts for a FORTRAN program, the program statement and introductory comments, declaration of variables and the code itself. ********** 1) The program statement and introductory comments ********** -------------------------------------------------- *** A) Comment statements *** c c Col 1 comment (c, C or !) ! you can put a ! after a line of code and the rest of the line will be ! treated as a comment statement, ie "a=a+1 !increment a" c Cols 2 through 5 are reserved for statement numbers c Cols 7 through 72 are used for FORTRAN statements c Col 6 is for continution marks. If your FORTRAN statement c is longer than 72-7=55 spaces long then any character in column c 6 means this line is continuation of previous line. *** B) Program statement *** c++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ c program addup c c++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ c ********** 2) Declarations ********** --------------- c Always start with "implicit none". That forces you to declare every c variable you use so compiler will help find spelling and other errors. c c Here are examples of declarations c implicit none c integer i,j,k real*4 coeff1, coeff2, coeff3 !"real*4" is the same as "real" but you're ! forced to know that the variable takes !up 4 bytes. this may seem pedantic, but !it's useful in debugging real*4 dist(100) !dimensioned variables, dist(1), dist(2), !dist(3)...dist(100) real*8 x,y !some of you have used "double precision" instead of real*8 !real*8 forces you to remember that a double precision number !takes up 8 bytes of memory, which is an aid for debugging character*80 filename logical first_time ********** 3) FORTRAN code ********** *** A) Examples of do loop syntax *** c Loops through to enddo, back to do, till i > 10 do i=1,10 lots of equations enddo c Loops through to enddo, back to do, increments i by 2 till i > 10 c In example above if no step size is given then defaults step size c of 1 is used. do i=1,10,2 lots of equations enddo c Example of nested do loop c sets i=1; does j=1,10 c then sets i=2; then does j=1,10 c and on and on do i=1,10 do j=1,10 fortran stuff enddo enddo *** B) Examples of "if" syntax *** c The relational operators are .gt. .lt. .ge. .le. .eq. .ne. if (i .lt. 17)a=5 if ((a-b) .gt. 10.)then bunch of fortran done when (a-b) > 10. elseif ((a-b) .gt. 5.) bunch of fortran done when 10. >= (a-b) > 5. else some other fortran done when (a-b) <= 5. endif if ((sin(d)-5.) .ne. 0.15)then whatever fortran you'd like endif *** C) Examples of arithmetic operations *** a=b i=j+1 b=b+1. !do math on right side of = and put it into variable on left dist(34)=a*3. i=i/j !NB: "integer arithmetic" is different from "real arithmetic" d=cos(a) !a is angle measured in radians a=mod(i,4) !the "remainder function". !if i=1,a=1; if i=2,a=2; if i=3,a=3; ! if i=4,a=0; if i=5,a=1; etc a=min(b,c) !a will = smaller value of b and c a=max(b,c) !a will = larger value of b and c c there are many other INTRINSIC FUNCTIONS. you can find them in FORTRAN BOOKS c and then need to know the syntax for your particular compiler call srand(some integer) a=rand(0) !getting random numbers *** D) Formatted input and output *** In general: read(unit,format)variables write(unit,format)variables unit: 1 through 4 are system defined (do not use) 5 is the keyboard 6 is the screen 7 through 999 can be defined by user. Default is file called fort.7, fort.8, etc unless open statement is used link unit to a file. The basic formats are "i" for integer "f" for floating point ("real") "e" for exponential "a" for character string "x" for skipping spaces "/" for new line read(5,*)a !read variable a from keyboard in free format write(6,*)a !write variable a to screen in free format write(6,*)'The average values are ',ave_1,' and ',ave_2 write(6,100)a !write a according to format give in line 100 100 format(' a = ',f10.5) !write string inside ' ' and then a in float format city_name='Tucson' write(13,"(' the city is ',a20)city_name open(10,file='list.dat') write(10,200)i,j,a,b 200 format(' i,j =',2i5,/,' a,b =',2e15.5) close(10) c c Example of reading line containing several values c integer rah,ram,decd,decm real ras,decs,mag,color character*6 number character*25 proper_name character*1 ds read(23,300)number,proper_name,rah,ram,ras,ds,decd,decm,decs,mag,color 300 format(a6,2x,a20,1x,i2,1x,i2,1x,f5.2,1x,a1,i2,1x,i2,1x,f4.1,1x,f5.2, $ 1x,f5.2) !This will read one line from unit 23 (file) which may look like: M120_5 RU Canis Venaticorum 02:12:12.12 -56:56:56.0 9.68 -1.23 !NB: $ in column 6 in format means line is continuation of previous line ***c as we teach you new FORTRAN we will add new pages to this cheat sheet ***