Basically, there are three ways to run an external prog - 1 - system. 2 - backticks. 3 - open a pipe.

system:

my $cmdToRun = "/path-to/the-c-prog";
system ($cmdToRun) && die "system $cmdToRun - $!\n";
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'system' just returns 0 on success and 1 on failure therefore you should test for it.

backticks:

my $cmdToRun = "/path-to/the-c-prog";
my @results = `$cmdToRun`;
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Using backticks is useful if you need to capture output from the program you are calling.

pipe:

my $cmdToRun = "/path-to/the-c-prog";
open (CMD, "$cmdToRun |") || die "open $cmdToRun - $!\n";
while (<CMD>) {
  # loop through the program output here...
}
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UPDATE Of course this assumes you meant calling an external c prog from within perl. After reading sniper's post I realize you could have meant running actual c code from within perl - in that case Inline.pm would be the natural choice.