it makes sens now.Thank you so much for this wonderfull explanation

"sizeof" works at compile time, and returns the size of the type you're referring to. Using "sizeof" with a string only works if the string is stack allocated: char example[45] = "this is an example.", using "sizeof" here would return 45, rather than the actual length of the string. "strlen" counts the number of characters passed until it reaches the NULL byte. So "strlen" can be used on dynamically or stack allocated strings and return the correct size.

why you used strlen insteed of sizeof i didnt get it here? when we do sizeof we wont get the size of the string?