PHP will automatically convert data types as necessary across the board - you need not worry about it happening. If you specifically wish to override PHP's type conversion, you can perform what is called a type cast - you forcibly convert a variable of type A to type B. In PHP, type casting looks like this:
At first, $mystring contains a string. However, we type cast it to be an integer, so PHP will convert it to an integer, and place the result into $myinteger. You can type cast as boolean using (bool), string using (string), and floating-point using (float).
Type casting is most often used to specifically enforce a type in order to provide extra security or just to make sure a set type of data is being used. For example, if your script absolutely requires an integer number, it's a smart move to typecast your variable with (integer) so that PHP will convert any other type to integer or do nothing if the type is already integer. Converting a float to an integer will automatically round the number down, and is actually faster than using the equivalent function.