0 CMATH(ROUND DOWN)EXIT END PROGRAM INT VOID EXIT(1); NONE CSTDLIBNO...

3.0 cmath(round down)exit End program int void exit(1); None cstdlibNone int rand( ) Varies cstdlibrand Random numberunsigned srand Set seedvoid srand(42); None cstdlibintfor randAll these predefined functions require using namespace std; as well as an include directive.

Notice that the previous call to

^pow

returns

^9.0

, not

⁹

. The function

^pow

always

arguments have a type

returns a value of type

^double

, not of type

^int

. Also notice that the function

^pow

requires two arguments. A function can have any number of arguments. Moreover,

every argument position has a specified type, and the argument used in a function call

should be of that type. In many cases, if you use an argument of the wrong type, some

automatic type conversion will be done for you by C++. However, the results may not

be what you intended. When you call a function, you should use arguments of the type

specified for that function. One exception to this caution is the automatic conversion

of arguments from type

^int

to type

^double

. In many situations, including calls to the

Predefined Functions 97

void

F

UNCTIONSA void function performs some action, but does not return a value. For a void function, a func-tion call is a statement consisting of the function name followed by arguments enclosed in paren-theses and then terminated with a semicolon. If there is more than one argument, the arguments are separated by commas. For a void function, a function invocation (function call) is a state-ment that can be used like any other C++ statement.

S

YNTAXFunction_Name(Argument_List);where the Argument_List is a comma-separated list of arguments:Argument_1, Argument_2, . . . , Argument_Last

E

^XAMPLEexit(1);

function

^pow

, you can safely use an argument of type

^int

(or other integer type) when

an argument of type

^double

(or other floating-point type) is specified.

Many implementations of

^pow

have a restriction on what arguments can be used. In

restrictionson pow

these implementations, if the first argument to

^pow

is negative, then the second argu-

ment must be a whole number. It might be easiest and safest to use

^pow

only when the

first argument is nonnegative.

■ PREDEFINED

void

FUNCTIONS

A

^void

function performs some action, but does not return a value. Since it performs

an action, a

^void

function invocation is a statement. The function call for a

^void

func-

tion is written similar to a function call for a function that returns a value, except that it

is terminated with a semicolon and is used as a statement rather than as an expression.

Predefined

^void

functions are handled in the same way as predefined functions that

return a value. Thus, to use a predefined

^void

function, your program must have an

include

directive that gives the name of the library that defines the function.

For example, the function

^exit

is defined in the library

^cstdlib

, and so a program

exit

that uses that function must contain the following at (or near) the start of the file:

#include <cstdlib>using namespace std;

The following is a sample invocation (sample call) of the function

^exit

:

98 Function Basics

T

HEexit

F

UNCTIONThe exit function is a predefined void function that takes one argument of type int. Thus, an invocation of the exit function is a statement written as follows:exit(Integer_Value);When the exit function is invoked (that is, when the above statement is executed), the program ends immediately. Any Integer_Value may be used, but by convention, 1 is used for a call to exit that is caused by an error, and 0 is used in other cases. The exit function definition is in the library cstdlib and it places the exit function in the stdnamespace. Therefore, any program that uses the exit function must contain the following two directives:

An invocation of the

^exit

function ends the program immediately. Display 3.3 con-

tains a toy program that demonstrates the

^exit

function.

Note that the function

^exit

has one argument, which is of type

^int

. The argument

is given to the operating system. As far as your C++ program is concerned, you can use

Display 3.3 A Function Call for a Predefined void Function1 #include <iostream>This is just a toy example. It 2 #include <cstdlib>would produce the same output 3 using namespace std;if you omitted these lines.4 int main( )5 {6 cout << "Hello Out There!\n";7 exit(1);8 cout << "This statement is pointless,\n"9 << "because it will never be executed.\n"10 << "This is just a toy program to illustrate exit.\n";11 return 0;12 }SAMPLE DIALOGUEHello Out There!

Predefined Functions 99

any

int

value as the argument, but by convention,

1

is used for a call to

exit

that is

caused by an error, and

0

is used in other cases.

A

^void

function can have any number of arguments. The details on arguments for

void

functions are the same as they were for functions that return a value. In particular,

if you use an argument of the wrong type, then, in many cases, some automatic type

conversion will be done for you by C++. However, the results may not be what you

intended.

Self-Test Exercises