More on Arguments and Parameters

To specify in a function definition that the function requires data to perform its task, you place additional information in the function’s parameter list, which is located in the parentheses following the function name. The parameter list may contain any number of parameters, including none at all (represented by empty parentheses as in Fig. 3.1, line 12) to indicate that a function does not require any parameters. The displayMessage member function’s parameter list (Fig. 3.3, line 13) declares that the function requires one parameter. Each parameter specifies a type and an identifier. The type string and the identifier courseName indicate that member function displayMessage requires a string to perform its task. The member function body uses the parameter courseName to access the value that’s passed to the function in the function call (line 33 in main). Lines 15–16 display parameter courseName’s value as part of the welcome message. The parameter variable’s name (courseName in line 13) can be the same as or different from the argument variable’s name (nameOfCourse in line 33)—you’ll learn why in Chapter 6.

A function can specify multiple parameters by separating each from the next with a comma. The number and order of arguments in a function call must match the number and order of parameters in the parameter list of the called member function’s header. Also, the argument types in the function call must be consistent with the types of the corresponding parameters in the function header. (As you’ll learn in subsequent chapters, an argument’s type and its corresponding parameter’s type need not always be identical, but they must be “consistent.”) In our example, the one string argument in the function call (i.e., nameOfCourse) exactly matches the one string parameter in the member-function definition (i.e., courseName).