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It is something of an axiom that any recursive solution can be rewritten as an iterative one. Often a finite infinite loop is useful:

```#!/usr/bin/perl -w

use constant HIGH => 10_000;
my \$ans = int(rand(HIGH)) + 1;
my ( \$lower, \$higher ) = (1, HIGH);
while(1) {
my \$guess = int((\$lower + \$higher)/2);
print "Guessing: \$guess\n";
last if \$ans == \$guess;
if ( \$guess > \$ans ) {
print "Lower...";
\$higher = \$guess -1;
}
else {
print "Higher...";
\$lower = \$guess +1;
}
}
print "The guess was correct!";

FWIW, with your code &function(args) syntax is not considered best style, you can drop the & - which you actually do in the sub. A consistent style is a good idea. You could declare and set \$ans in one call.

It is worth noting that while an iterative solution will almost inevitably run faster than a recursive solution, a good recursive solution is often quite terse. A classic very simple example is the calculation of factorial n! The factorial is defined n! = 1 x 2 x 3 x .... (n-1) x n You can code using either iteration or recursion.....

```sub fact_rec{
my (\$num) = @_;
\$num ? \$num*fact_rec(\$num-1) : 1
}

sub fact_it{
my (\$num) = @_;
my \$fac = 1;
for my \$i( 1 .. \$num ) {
\$fac *= \$i;
}
return \$fac;
}

for (1..10){
printf"%d!\t%10d\t%10d\n", \$_, fact_rec(\$_), fact_it(\$_);
}

As you can see the recursive solution is short and sweet. It also has a bug that can cause it to go infinite. One gotcha with recursion is that you need to be *positive* that your exit condition (ie stop recursing when we are done) will be *always* be met. A typical real world use for recursion is in dealing with tree like structures
 The bug: Negative numbers or floats mean that \$num -1 will never equal 0, and so always it will always be true.

cheers

tachyon

In reply to Re: Behold! The power of recursion. by tachyon
in thread Behold! The power of recursion. by DigitalKitty

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