Formal parameters, like variables, are of a specific data type. In the following syntax example, the data type appears after each formal parameter name:
Show_Window(window_name IN CHAR,
x IN NUMBER,
y IN NUMBER);
Return BOOLEAN
You can see from this example that the function SHOW_WINDOW takes parameters of type CHAR, and NUMBER. CHAR and NUMBER are native PL/SQL types.
In a call to a Built-in subprogram, an actual parameter can be any expression that evaluates to a value of the same type as the formal parameter to which it corresponds. This means that an actual parameter can be a local or global variable, a function, or any combination of variables, constants, and operators that evaluates to a value of the appropriate type.