an issue with my dob sorting script - bash

Question

I am getting the error: line 34: #10#1001: syntax error: operand expected (error token is "#10#1001")
I have just changed
[! -f INPUT ] &
to
[ ! -f INPUT ] &&
and now i am getting the error
line 34: #10#1001: syntax error: operand expected (error token is "#10#1001")
when i run the script.
The script inputs users names, phones numbers and dob and then sorts the infomation and calculates their ages.
What could be causing this error as i cannot work out what operand it is demanding
#!/bin/bash
a=0
while [ $a -lt 2 ];
do
echo Please enter a first name
read firstName
echo Please enter last name
read lastName
echo Please enter phone number
read phoneNumber
echo Please enter date of birth - format dd/mm/yyyy
read dob
echo "$firstName,$lastName,$phoneNumber,$dob" >> userBirthdays.csv
echo If you would like to add another person press 1 or enter 2 to proceed
read a
done
INPUT=./userBirthdays.csv
OLDIFS=$IFS
IFS=","
[ ! -f INPUT ] && while read while read Name Surname Telephone DOB
do
birthMonth=${DOB:0:2}
birthDay=#10${DOB:3:2}
birthYear=${DOB:6:4}
currentDate=`date +%d/%m/%Y`
currentMonth=${currenDate:0:2}
currentDay=#10${currentDate:3:2}
currentYear=${currentDate:6:4}
if [[ "$currentMonth" -lt "$birthMonth" ]] || [[ "$currentMonth" -eq "$birthMonth" && "$((#10$currentDay))" -lt "$((#10$birthDay))" ]]
then
let Age=currentYear-birthYear-1
else
let Age=currentYear-birthYear
fi
echo "Name : $Name"
echo "Surname : $Surname"
echo "Telephone : $Telephone"
echo "DOB : $DOB"
echo "Age : $Age"
echo "##########################################"
done < $INPUT
IFS=$OLDIFS
echo $DATE
exit 0;

Answer 1

You have two mistakes on this line:
[ ! -f INPUT ] && while read while read Name Surname Telephone DOB
It should be:
[ -f ${INPUT} ] && while read Name Surname Telephone DOB
I recommend debugging your script with:
bash -x /path/to/birthdays.bash
This will print command traces before executing each command.

Answer 2

-lt comparison (and friends) are for integers, not strings. And you turn currendDay into a non-integer string by prepending #10 to it (you do it twice, by the way).
Your intentions here are not very clear. Do you want to compare strings? Then use < instead of -lt. Do you want currentDay to be a number? Then don't prepend #10 to its value (in both places you do it now).