Shell Programming and Scripting

I'm relatively new to both UNIX and Linux and slightly less new at programming. But I can't figure out why this won't run properly.

It's meant to calculate the GCD of two numbers (simple enough, you'd think). And I designed it myself and it looks good to me and my instructor won't respond. If anyone could help me out, it would be appreciated.


#! /bin/bash

#Takes arguments to determin the GCD

errorNum="Too many or too few arguments passed."
errorUse="Usage: $0 [decimal] [decimal]"
errorNeg="Cannot use a negative number."

checkIfZero ()
{
if [ $a=0 ]
then
drop=1
elif [ $b=0 ]
then
drop=1
else
drop=0
fi
exit 0
}

if [ $1 < 1 -o $2 < 1 ]
then
echo $errorNeg
echo $errorUse
exit 0
fi

if [ $# -le 1 -o $# -gt 2 ]
then
echo $errorNum
echo $errorUse
exit 0
elif [ $1 -ge 0 ] && [ $2 -ge 0 ]
then
a=$1
b=$2
drop=0
while [ $a -gt 0 ] || [ $b -gt 0 ]
do
if [ $a -gt $b ]
then
if [ drop -gt 0 ]
then
checkIfZero
c=`expr $a % $b`
a=$c
fi
elif [ $b -gt $a ]
then
if [ drop -gt 0 ]
checkIfZero
c=`expr $b % $a`
b=$c
fi
fi
done

if [ $a -gt $b ]
then
echo "The GCD is $a."
else
echo "The GCD is $b."
fi
fi

We have a special homework forum. Please post over there. I would move the thread but it the homework forum requires a special kind of post.

Thank you.