Fortran语法（子例程的声明）

Question

I try to read fortran (i think so) program and can`t understand beginning of subroutine. Its look like: I cant understand second block (red) - what is this? Parameters/arguments, global variable or something like that?

And yellow is looks like constant array, but language declaration is different in my manual.

Also i cant find declaration of IF like this:

Its a IF (condition) then goto less,eq,greater or something other?

Answer 1

You're looking at rather old fixed source form FORTRAN in which the position of characters on lines is significant. In particular any character (other than a 0 or a blank) in column 6 indicates that the line is a continuation of the previous line. A C in column 1 indicates a comment.

Strange IF statement first

IF( HP(IM) - 70. ) 105,105,110

is an arithmetic if statement. If HP(IM)-70 is negative, go to line labelled 105 , if zero go to line labelled 105 , if positive to line labelled 110 . Your posting doesn't show those lines, the labels are in columns 1-5 of a line.

Now red

COMMON

introduces a common block whose name, if any, then follows enclosed in / / . There then follows a list of the variables in the common block. In your code the declarations of common blocks CONTRL , ALPHA and DON are spread across lines.

Your code suggests that the common blocks are being used to pass variables to/from the subroutine without using its argument list. There is probably a program scope with the same common blocks declared, the same common blocks may appear in other subroutines too. Don't be surprised if the other scopes have common blocks with the same names but apparently different contents, one of the nefarious uses of common blocks was to fiddle around with variable names. Even more fun, a variable which is a 4-byte integer in one scope can be treated as a 4-byte real in another scope.

Now green

DATA TME / ... /

initialises the array TME with the values between / and / .