However, remember that the binary number string is built by calculating the remainder of input divided by 2 and concatenating that to the end.
After your call to decimalToBinary(), use the addition operator (+) to concatenate the remainder of input divided by 2 to the end of the string your recursive function returns. Also, wrap the operation in parentheses.
Teller, Thank you for your reply. Still have a problem even after removing quotation mark and second concatination. I just added concatination mark (+) with input modul of 2. still not working.