fact(4) = 4 * 3 * 2 * 1 = 24

##</code><code>##

$ perl -e '
sub fact { 
     my $c = shift; 
     my $result = 1; 
     $result *= $_ for 1..$c; 
     return $result;}  
print fact (shift);' 10
3628800

##</code><code>##

fact(1) = 1
fact (n) = n * fact (n-1)

##</code><code>##

$ perl -e '
sub fact { 
     my $c = shift; 
     return 1 if $c == 1; 
     $c * fact($c-1);
} 
print fact (shift);' 10
3628800