Batch file loop and increment value for condition

I am trying to have the below batch file do following two things:

1. only allow the values YES,yes,Y,y, or NO,no,N,n

2. increment the counter %var1 only if answer to question 2 is "y" and not able to get the syntax correct. If %var1%=1 then I am trying to display function :end . Thank you :).

Question 2

  set /P c=Do you want to send the DOSE report[y/n]? 

Batch file as is:

@ECHO OFF
:: ask user 
 :choice
 set /P c=Has the check been done [y/n]
 if /i %c%==y (
 set /P c=Do you want to send the DOSE report[y/n]?
 ) else (
 if /i %c%==n goto check
 )
 :file
 if /i %c%==y ( 
 "L:\NGS\HLA LAB\total quality management\QC & QA\DOSE reports\DOSE reporting form.xlsm"
 ) else (
 if /i %c%==n goto goodbye
 )
 :check
 set /P c=Do you want to perform the check [y/n]
 if /i %c%==y (
 set /P c=please complete the check and click enter
 goto file
 ) else (
 if /i %c%==n goto goodbye
 )
 :goodbye
echo "goodbye"
TIMEOUT 2 /nobreak
exit

:: count loop
set var1=0
:loop
set /a var1=%var1%+1
if %var1% EQU 1 (
    goto end
) else (
    goto loop
)
:goodbye
echo "goodbye"
TIMEOUT 2 /nobreak
exit
:end
echo "the DOSE report has already been sent by %USERNAME% on %DATE% at   %TIME%"