Sams Teach Yourself C++ in 21 Days

Organizing into Functions 105

5

Also note that the parameter names in the prototype are lengthand width, but the para-

meter names in the definition are lenand wid. As discussed, the names in the prototype

are not used; they are there as information to the programmer. It is good programming

practice to match the prototype parameter names to the implementation parameter names,

but as this listing shows, this is not required.

The arguments are passed in to the function in the order in which the parameters are

declared and defined, but no matching of the names occurs. Had you passed in

widthOfYard, followed by lengthOfYard, the FindArea()function would have used the

value in widthOfYardfor length and lengthOfYardfor width.

The body of the function is always enclosed in braces, even when it consists

of only one statement, as in this case.

NOTE

Execution of Functions ........................................................................................

When you call a function, execution begins with the first statement after the opening

brace ({). Branching can be accomplished by using the ifstatement. (The ifand other

related statements will be discussed on Day 7, “More on Program Flow.”) Functions can

also call other functions and can even call themselves (see the section “Recursion,” later

today).

When a function is done executing, control is returned to the calling function. When the

main()function finishes, control is returned to the operating system.

Determining Variable Scope ................................................................................

A variable has scope, which determines how long it is available to your program and

where it can be accessed. Variables declared within a block are scoped to that block; they

can be accessed only within that block’s braces and “go out of existence” when that

block ends. Global variables have global scope and are available anywhere within your

program.

Local Variables ..............................................................................................

Not only can you pass in variables to the function, but you also can declare variables

within the body of the function. Variables you declare within the body of the function are

called “local” because they exist only locally within the function itself. When the func-

tion returns, the local variables are no longer available; they are marked for destruction

by the compiler.