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224 10 Transforming with Traditional Programming Languages

use this list like any other. For example, the following program will print the

statistics for two of the columns of the database:

while (<>) {

chomp;

push(@table, [split]);

}

($mean, $var) = stats(1);

print("Statistics for column 1:");

print(" mean $mean variance $var\n");

($mean, $var) = stats(4);

print("Statistics for column 4:");

print(" mean $mean variance $var\n");

Of course, the program above has yet another opportunity for a procedure;

namely, one that prints the statistics:

sub printstats {

my $column = $_[0];

my ($mean, $var) = stats($column);

print("Statistics for column $column:");

print(" mean $mean variance $var\n");

}

One cannot help but notice that the scalar$_and the array@_are used

frequently in Perl. Because of this it is a good idea to assign the parameters

of a procedure to variousmyvariables belonging to the procedure as soon as

possible. It also makes it much easier for a person to understand what a pro-

cedure is supposed to do. In this case,$columnis a lot more understandable

than$_[0].

Putting all of this together, one obtains the solution to the task in pro-

gram 10.8.

The procedure definitions can go either before the main program or after it.

Summary

• A procedure is a collection of statements that can be performed as a unit.


• A procedure is invoked by using its name and giving a list of parameters.

•Amyvariable is limited to the part of the program in which it is declared.