Integer Expression Expected!?!?

Ok, so I am beggining a script to factor the time difference from when a user logs on to current time but before I can even get too far I am getting the INTEGER EXPRESSION EXPECTED error. Can someone tell me what I am doing wrong?

lhour=$(who | grep "$1" | cut -c30,31);
lmin=$(who | grep "$1" | cut -c33,34);
chour=$(date | cut -c12,13);
cmin=$(date | cut -c15,16);
hrs;
if [ "$chour" -ge "$lhour" -a "$lmin" -gt "$cmin" ]
then
hrs=0
fi

echo "chour $chour";
echo "lhour $lhour";
echo "cmin $cmin";
echo "lmin $lmin";
echo "hours $hrs";

Mostly the $hour and $min fields are not getting the numeric, so in the If conditions -gt and -ge not able to do comparison with those field .