SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
After all input or output to a unit has been completed and the unit is no longer required, the link
between the SIMSCRIPT II.5 logical unit and the physical device, as controlled by the operating
system, may be removed by closing the unit. This is achieved by a statement of the form:
close unit device
If the device is the current input or output unit, then that unit (read.v or write.v) is reset to its
default value. Note that at the completion of a SIMSCRIPT II.5 program, all files used or opened
during the course of the program run will be closed automatically by SIMSCRIPT II.5.
3.5.2 End-of-File Conditions
Whenever a read statement is executed, there is the possibility of reading data from an "empty"
file or reaching the end of the data file, which is referred to as an end-of-file condition. The freeform
read statement, as previously noted, provides a check for an end-of-file condition through the
statement if data is ended. A similar check is needed for formatted I/O.
A SIMSCRIPT II.5 system-defined variable, eof.v, is maintained for each logical input unit. A
reference to eof.v applies always to the value of the current logical unit, set by use. This variable
is initialized to zero when a unit is first referenced. When an end-of-file condition is encountered
by a read statement, the SIMSCRIPT II.5 system refers to the eof.v variable for direction. If
eof.v is still equal to zero, encountering the end-of-file condition is considered an error, and the
program terminates with an error message. If, however, under program control, the eof.v variable
has previously been assigned the value 1, the variables in the read list are assigned values of
zero, the eof.v variable is set to 2, and control returns to the statement following the read. In
other words, setting the value of eof.v to 1 is considered a message to the SIMSCRIPT II.5 system
to the effect, "Do not terminate the program; return zero values and indicate that the end-of-file
marker has been encountered." By testing eof.v after a read statement, the program logic can
determine whether the statement read true data or encountered an end-of-file marker. This facility
can be used in the following ways:
1. As an end of data signal:
use unit 1 for input
let eof.v = 1
.
while eof.v ne 2,
do
read Z as I 2
add Z to SUM
add 1 to COUNTER
loop
write COUNTER, SUM/COUNTER as "The Average of", I 4,
"Items Processed Is", D(6,2)
stop
end
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