Php error : Unknown database while connection

Question

Getting this error when i am using variable which have the name of the database on the place of database name :

$con=mysqli("localhost" , "root" , " " , $databaseName);

Not getting the error when i am typing the name of the database :

$con=mysqli("localhost" , "root" , " ", "praveensoni");

Answer 1

Since we cannot see the full code, im gonna assume your variable is not seen by the function, pay attention to the scope and where you gave it a value before using it

Answer 2

Dominique Abou Samah its showing the variable value that contains the name of the database.
I am not able to show you the picture of the error here since Sololearn doesn't give this facility.