Parameters and Arguments

Arguments are the initializers for a function’s parameters. The first argument initializes the first parameter, the second argument initializes the second parameter, and so on. Although we know which argument initializes which parameter, we have no guarantees about the order in which arguments are evaluated (§ 4.1.3, p. 137). The compiler is free to evaluate the arguments in whatever order it prefers.

The type of each argument must match the corresponding parameter in the same way that the type of any initializer must match the type of the object it initializes. We must pass exactly the same number of arguments as the function has parameters. Because every call is guaranteed to pass as many arguments as the function has parameters, parameters are always initialized.

Because fact has a single parameter of type int, every time we call it we must supply a single argument that can be converted (§ 4.11, p. 159) to int:

fact("hello");       // error: wrong argument type
fact();              // error: too few arguments
fact(42, 10, 0);     // error: too many arguments
fact(3.14);          // ok: argument is converted to int

The first call fails because there is no conversion from const char* to int. The second and third calls pass the wrong number of arguments. The fact function must be called with one argument; it is an error to call it with any other number. The last call is legal because there is a conversion from double to int. In this call, the argument is implicitly converted to int (through truncation). After the conversion, this call is equivalent to

fact(3);