/NUMBER CUSTOMERS. IF NUMBER IS 0, ONLY AN ERROR MESSAGE IS OUTPUT....

5 //number customers. If number is 0, only an error message is output.6 int main( )7 {8 int number;9 double totalWeight;10 cout << "Enter the number of customers: ";11 cin >> number;12 cout << "Enter weight of ice cream to divide (in ounces): ";13 cin >> totalWeight;14 iceCreamDivision(number, totalWeight);15 return 0;16 }17 void iceCreamDivision(int number, double totalWeight)18 {19 double portion;20 if (number == 0)21 {22 cout << "Cannot divide among zero customers.\n";23 return;If number is 0, then thefunction execution ends here.24 } 25 portion = totalWeight/number;26 cout << "Each one receives " 27 << portion << " ounces of ice cream." << endl;28 }SAMPLE DIALOGUEEnter the number of customers: 0Enter weight of ice cream to divide (in ounces): 12Cannot divide among zero customers.

Programmer-Defined Functions 115

returned by the function. For a function that changes the value of some argument vari-

ables, the postcondition will describe all the changes made to the values of the arguments.

For example, the following is a function declaration with precondition and post-

condition:

void showInterest(double balance, double rate);//Precondition: balance is a nonnegative savings account balance. //rate is the interest rate expressed as a percentage, such as 5 for 5%.//Postcondition: The amount of interest on the given balance //at the given rate is shown on the screen.

You do not need to know the definition of the function

showInterest

in order to use

this function. All that you need to know in order to use this function is given by the

precondition and postcondition.

When the only postcondition is a description of the value returned, programmers

usually omit the word

Postcondition

, as in the following example:

double celsius(double fahrenheit);//Precondition: fahrenheit is a temperature in degrees Fahrenheit.//Returns the equivalent temperature expressed in degrees Celsius.

Some programmers choose not to use the words precondition and postcondition in

their function comments. However, whether you use the words or not, you should

always think in terms of precondition and postcondition when designing a function

and when deciding what to include in the function comment.

■

main

IS A FUNCTION

As we already noted, the

main

part of a program is actually the definition of a function

called

main

. When the program is run, the function

main

is automatically called; it, in

turn, may call other functions. Although it may seem that the

return

statement in the

main

part of a program should be optional, practically speaking it is not. The C++ stan-

dard says that you can omit the

return 0

statement in the

main

part of the program,

but many compilers still require it and almost all compilers allow you to include it. For

the sake of portability, you should include

return 0

statement in the

main

function.

You should consider the

main

part of a program to be a function that returns a value of

type

int

and thus requires a

return

statement. Treating the

main

part of your program

as a function that returns an integer may sound strange, but that’s the tradition which

many compilers enforce.

Although some compilers may allow you to get away with it, you should not include

a call to

^main

in your code. Only the system should call

^main

, which it does when you

run your program.

116 Function Basics

■ RECURSIVE FUNCTIONS

C++ does allow you to define recursive functions. Recursive functions are covered in

Chapter 13. If you do not know what recursive functions are, there is no need to be

concerned until you reach that chapter. If you want to read about recursive functions

early, you can read Sections 13.1 and 13.2 of Chapter 13 after you complete Chapter 4.

Note that the

main

function should not be called recursively.

Self-Test Exercises