7.  Program Form

7.1.  Blank Lines

• Completely blank lines are now legal comment lines.

7.2.  Program and Block Data Statements

• A main program may now begin with a statement that gives that program an external name:

  program work
  

  Block data procedures may also have names.

  block data stuff
  

  There is now a rule that only one unnamed block data procedure may appear in a program. (This rule is not enforced by our system.) The Standard does not specify the effect of the program and block data names, but they are clearly intended to aid conventional loaders.

7.3.  ENTRY Statement

• Multiple entry points are now legal. Subroutine and function subprograms may have additional entry points, declared by an entry statement with an optional argument list.

  entry extra(a, b, c)
  

  Execution begins at the first statement following the entry line. All variable declarations must precede all executable statements in the procedure. If the procedure begins with a subroutine statement, all entry points are subroutine names. If it begins with a function statement, each entry is a function entry point, with type determined by the type declared for the entry name. If any entry is a character-valued function, then all entries must be. In a function, an entry name of the same type as that where control entered must be assigned a value. Arguments do not retain their values between calls. (The ancient trick of calling one entry point with a large number of arguments to cause the procedure to ``remember'' the locations of those arguments, then invoking an entry with just a few arguments for later calculation, is still illegal. Furthermore, the trick doesn't work in our implementation, since arguments are not kept in static storage.)

7.4.  DO Loops

• do variables and range parameters may now be of integer, real, or double precision types. (The use of floating point do variables is very dangerous because of the possibility of unexpected roundoff, and we strongly recommend against their use). The action of the do statement is now defined for all values of the do parameters. The statement

  do 10 i = l, u, d
  

  performs iterations. The do variable has a predictable value when exiting a loop: the value at the time a goto or return terminates the loop; otherwise the value that failed the limit test.

7.5.  Alternate Returns

• In a subroutine or subroutine entry statement, some of the arguments may be noted by an asterisk, as in

  subroutine s(a, *, b, *)
  

  The meaning of the ``alternate returns'' is described in section 5.2 of the Appendix.