Hi,
Do you konw how should Ackermann function look in bash or sh, or any diffrent shell laguage ??
I know this function i c++ but I don't know enough shell language

Thanks for any help

Reference for those who don't know what the Ackermann function is:link

I am assuming you are doing this to take a recursive algorithm that you know and learn more about shell scripting by rewriting in bash or sh?

Certainly you are not doing it for performance ;-}

There is a group of Ackermann functions written in many different languages here:

Ackermann's Function

The closest to shell form would be the Perl version.

That looks like this:

#!/usr/bin/perl
use strict;
use integer;

sub Ack {
    my($M, $N) = @_;
    return( $N + 1 )         if ($M == 0);
    return( Ack($M - 1, 1) ) if ($N == 0);
    Ack($M - 1, Ack($M, $N - 1));
}

my $NUM = $ARGV[0];
$NUM = 1 if ($NUM < 1);
my $ack = Ack(3, $NUM);
print "Ack(3,$NUM): $ack\n\n";

#!/bin/bash

#Uncomment the 'set' if you want a line-by-line result...
#set -x   

ack ()
{
	local m=$1
	local n=$2
	if [ $m -eq 0 ] 
	   then
		return $(( $n+1 )) 
	fi

	if [ $n -eq 0 ] 
	   then
		ack $(( $m-1 )) 1
		return $?
	fi
	
	ack $m $(( $n-1 ))
	ack $(( $m-1 )) $? 
}
loops=0
p=$1
o=3
(( num = p<1?1:$p ))

ack $o $num 
printf "ack %s %s = %s  \n\n" $o $num $?

Ok. As an exercise, I have:

#!/bin/bash

function ack
{
  local m=$1 n=$2

  if ((m == 0)); then let r=n+1
  elif ((n == 0)); then ack $((m-1)) 1
  else
    ack $m $((n-1))
    ack $((m-1)) $r
  fi
}               
        
ack $1 $2
echo "ack($1, $2) =" $r

Great answer!