SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
Figure 2-5c illustrates a more complex situation in which a main routine and three subprograms
interact. Subprograms 1 and 2 are both called and calling routines: They are called by the main
routine and, in turn, they call on subprogram 3. The call of subprogram 1 or 2 by the main routine
is the first level of calling. The call of subprogram 3 by subprograms 1 and 2 while under the control
of the main routine is a second level. In general, there can be any level of calling in effect within
a program at any time. The calling rules do not change from level to level. Control always passes
from a calling to a called program and back again. Whether there are many intermediate calls and
returns between an original call on a subprogram and a return to its calling program is insignificant.
If A calls B and B calls C, then C must return control to B before B can return to A. A subprogram
cannot return control to any routine other than the one that called it. For example, C cannot return
control directly to A.
MAIN PROGRAM
SUBPROGRAM1
SUBPROGRAM 3
SUBPROGRAM SUBPROGRAM 2 3
END
Figure 2-5c. Program Consisting of Three Subprograms and a Main Routine
2.10 Routine Definition
A SIMSCRIPT II.5 program may be composed of several program sections: a preamble (data declaration)
section, a main routine, and a number of subprograms. Statements are needed to delimit
these program components. As already noted, the variable declaration section is headed by the
word preamble and terminated by the word end.
The statements that make up the main routine should be preceded by the one-word statement:
main
This is not strictly necessary. Since all other sections of a program must have a heading, it is possible
to omit the main statement and assume that statements belong to the main routine if not otherwise
labeled. Nevertheless, it is good programming practice to label program sections fully. Each
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