I think he means doubt. Would probably have been better to say he has “1 question”.
If you’d tried googling you would have found the answer in a matter of seconds.
Boolean variables can be true or false (no quotes, all lower case).
You can also use 1 and 0 instead of true or false,
This forum is for Blynk related questions. Yours is a basic C/C++ programming question and doesn’t need to be asked here.
If your coding knowledge is poor enough that you have to ask this question, and your inability to help yourself is such that you come here to ask the question rather than googling it, then you are likely to have many Blynk specific questions along the way. My advice would be to save up your ‘good will’ credits and use them wisely rather than asking basic programming questions here.