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Full Discussion: Palindrometer Program
Homework and Emergencies Homework & Coursework Questions Palindrometer Program Post 302543299 by methyl on Saturday 30th of July 2011 07:24:48 PM
Old 07-30-2011
I agree with the above posters. We need to know precisely what Operating System you have and exactly what Shell you have. Nowadays it is quite rare to encounter a raw Bourne Shell.
The palindrone question is an advanced text manipulation exercise which usually requires you to first determine the length of the string, then reverse the order of the characters in the string, and then compare the before and after string. If they are the same then it is a palindrome.
There are some extraordinarily complex methods for doing this involving arrays however it may be worth checking out the unix "rev" command if this command is allowed by your tutor.

This example script should work with any true Bourne Shell.
Code:
string="abba"
string_rev="`echo "${string}"|rev`"
if [ "${string}" = "${string_rev}" ]
then
    echo "Palindrome: ${string}"
fi


Ps. The straightforward answer to the original question is "zero". I do hope that this isn't an interview question.
However if you continue from 100001 and attempt to find the next palindrone (which I guess is 101101) by incremental methods then this is much more interesting.


Conforming to old Bourne Shell syntax we arrive at something like this:

Code:
counter="100001"
while true
do
        counter=`expr ${counter} + 1`
        reverse=`echo "${counter}"|rev`
        echo "${counter} ${reverse}"
        if [ "${counter}" = "${reverse}" ]
        then
                echo "Palindrone: ${counter} ${reverse}"
                break
        fi
done
# Deliberately ignored the requirement to return either 1 or 979 but this is trivial.
# Also deliberately avoided the requirement for the initial mileage to be a parameter. The core code is to find out the next palindrone

If your course context suggests that the string reversal bit should be done with string arrays, then it is up to you to how you reverse the string.

Last edited by methyl; 07-30-2011 at 09:24 PM.. Reason: Wrong guess.
 

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INTVAL(3)								 1								 INTVAL(3)

intval - Get the integer value of a variable

SYNOPSIS
int intval (mixed $var, [int $base = 10]) DESCRIPTION
Returns the integer value of $var, using the specified $base for the conversion (the default is base 10). intval(3) should not be used on objects, as doing so will emit an E_NOTICE level error and return 1. PARAMETERS
o $var - The scalar value being converted to an integer o $base - The base for the conversion Note If $base is 0, the base used is determined by the format of $var: o if string includes a "0x" (or "0X") prefix, the base is taken as 16 (hex); otherwise, o if string starts with "0", the base is taken as 8 (octal); otherwise, o the base is taken as 10 (decimal). RETURN VALUES
The integer value of $var on success, or 0 on failure. Empty arrays return 0, non-empty arrays return 1. The maximum value depends on the system. 32 bit systems have a maximum signed integer range of -2147483648 to 2147483647. So for example on such a system, intval('1000000000000') will return 2147483647. The maximum signed integer value for 64 bit systems is 9223372036854775807. Strings will most likely return 0 although this depends on the leftmost characters of the string. The common rules of integer casting apply. EXAMPLES
Example #1 intval(3) examples The following examples are based on a 32 bit system. <?php echo intval(42); // 42 echo intval(4.2); // 4 echo intval('42'); // 42 echo intval('+42'); // 42 echo intval('-42'); // -42 echo intval(042); // 34 echo intval('042'); // 42 echo intval(1e10); // 1410065408 echo intval('1e10'); // 1 echo intval(0x1A); // 26 echo intval(42000000); // 42000000 echo intval(420000000000000000000); // 0 echo intval('420000000000000000000'); // 2147483647 echo intval(42, 8); // 42 echo intval('42', 8); // 34 echo intval(array()); // 0 echo intval(array('foo', 'bar')); // 1 ?> NOTES
Note The $base parameter has no effect unless the $var parameter is a string. CHANGELOG
+--------+---------------------------------------------------+ |Version | | | | | | | Description | | | | +--------+---------------------------------------------------+ | 5.1.0 | | | | | | | Throws E_NOTICE and returns 1, when an object is | | | passed to $var. | | | | +--------+---------------------------------------------------+ SEE ALSO
boolval(3), floatval(3), strval(3), settype(3), is_numeric(3), Type juggling, BCMath Arbitrary Precision Mathematics Functions. PHP Documentation Group INTVAL(3)
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