Sams Teach Yourself C++ in 21 Days

Organizing into Functions 121

5

59:

60: double Double(double original)

61: {

62: cout << “In Double(double)\n”;

63: return 2 * original;

64: }

myInt: 6500

myLong: 65000

myFloat: 6.5

myDouble: 6.5e+20

In Double(int)

In Double(long)

In Double(float)

In Double(double)

DoubledInt: 13000

DoubledLong: 130000

DoubledFloat: 13

DoubledDouble: 1.3e+21

The Double()function is overloaded with int,long,float, and double. The

prototypes are on lines 5–8, and the definitions are on lines 42–64.

Note that in this example, the statement using namespace std;has been added on line

10, outside of any particular function. This makes the statement global to this file, and

thus the namespace is used in all the functions declared within this file.

In the body of the main program, eight local variables are declared. On lines 14–17, four

of the values are initialized, and on lines 29–32, the other four are assigned the results of

passing the first four to the Double()function. Note that when Double()is called, the

calling function does not distinguish which one to call; it just passes in an argument, and

the correct one is invoked.

The compiler examines the arguments and chooses which of the four Double()functions

to call. The output reveals that each of the four was called in turn, as you would expect.

Special Topics About Functions ..........................................................................

Because functions are so central to programming, a few special topics arise that might be

of interest when you confront unusual problems. Used wisely, inline functions can help

you squeak out that last bit of performance. Function recursion is one of those wonder-

ful, esoteric bits of programming, which, every once in a while, can cut through a thorny

problem otherwise not easily solved.

OUTPUT

LISTING5.8 continued

ANALYSIS