Dear Indu,
What I understand from your query is that your company provides casual leave to people on probation, and you also have it. Your query pertains to the month in which you joined, as you joined in the middle of the month. Therefore, if you joined before or on the 15th of that month, you will get the leave for that month; otherwise, you won't. I have also seen some companies providing half casual leave and calculating it on a prorate basis.
Kind regards