#! /usr/bin/perl -w
#
# sigfigs.pl - Compute the significant digits in a number.
#
# Created by Neil J. Gunther, Tue Jun  4 22:55:41  2002


# Read the number in from the keyboard.
print "Enter a number: ";
$numstring = <STDIN>;
chomp($numstring); # Toss the carriage return
$skipzero = ''; $i = 0;

if ($numstring =~ /\./) { # Check for presence of decimal point.
        ($int, $frac) = split(/\./, $numstring); # Separate integer and fractional parts
        $digstring = $int . $frac; # Concatenate sans decimal point
        $numfigs = length($digstring);
        while ($i < $numfigs ) {  # Find position of first non-zero digit
                # Compare FORWARDS from LEFTmost digit...
                if ($digstring =~ /^$skipzero(\d)/) {
                        $sigfigs = $numfigs - $i;
                        last if ($1 ne '0');
                }
                $skipzero = $skipzero . '.'; 
                $i++;
        }
} 
else {  # No decimal point, so just scan the integer...
        $numfigs = length($numstring);
        while ($i < $numfigs) {  # Find position of first non-zero digit
                # Compare BACKWARDS from RIGHTmost digit...
                if ($numstring =~ /(\d)$skipzero$/) {
                        $sigfigs = $numfigs - $i;
                        last if ($1 ne '0');
                }
                $skipzero = $skipzero . '.'; 
                $i++;
        }
}

# Print out the result.
print "The number '$numstring' contains $sigfigs significant digits.\n";