Fundamentals of Programming - Sharifce.sharif.edu/courses/92-93/1/ce153-1/resources/root...Fundamentals of Programming Session 23 These slides have been created using Deitel’sslides

Fall 2013

Instructor: Reza Entezari-Maleki

Email: [email protected]

Sharif University of Technology 1

Fundamentals of Programming Session 23

These slides have been created using Deitel’s slides

Outlines

C++

Inline Functions

References and Reference Parameters

Default Arguments

Classes and Objects

Defining a Member Function with a Parameter

Data Members, set Functions and get Functions

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C++ improves on many of C’s features and provides

object-oriented-programming (OOP) capabilities that

increase software productivity, quality and reusability.

This section revisits the addition program of Fig. 2.8

and illustrates several important features of the C++

language as well as some differences between C and

C++.

C file names have the .c (lowercase) extension.

C++ file names can have one of several extensions, suchas .cpp, .cxx or .C (uppercase).

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C++

The C++ Standard Library is divided into many

portions, each with its own header file.

The header files contain the function prototypes for

the related functions that form each portion of the

library.

The header files also contain definitions of various

class types and functions, as well as constants

needed by those functions.

Figure 15.2 lists common C++ Standard Library

header files.4

Header Files

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Header Files …

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C++ …

Implementing a program as a set of functions is good

from a software engineering standpoint, but function calls

involve execution-time overhead.

C++ provides inline functions to help reduce function call

overhead—especially for small functions.

The trade-off is that multiple copies of the function code

are inserted in the program (often making the program

larger) rather than there being a single copy of the

function to which control is passed each time the function

is called.

The compiler can ignore the inline- qualifier and

typically does so for all but the smallest functions.7

Inline Functions

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Inline Functions …

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Lines 4–6 are using statements that help us eliminate

the need to repeat the std:: prefix.

From this point forward, each C++ example contains one

or more using statements.

In place of lines 4–6, many programmers prefer to use

using namespace std;

C++ also provides type bool for representing boolean

(true/false) values.

The two possible values of a bool are the keywords trueand false.

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Two ways to pass arguments to functions in many

programming languages are pass-by-value and pass-by-

reference.

This section introduces reference parameters—the first of

two means that C++ provides for performing pass-by-

reference.

A reference parameter is an alias for its corresponding

argument in a function call.

For example, the following declaration in a function header

int &count

when read from right to left is pronounced ―count is a

reference to an int.‖11

References and Reference Parameters

In the function call, simply mention the variable by name

to pass it by reference.

Then, mentioning the variable by its parameter name in

the body of the called function actually refers to the

original variable in the calling function, and the original

variable can be modified directly by the called function.

As always, the function prototype and header must agree.

Figure 15.5 compares pass-by-value and pass-by-reference

with reference parameters.

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References and Reference Parameters …

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References can also be used as aliases for other

variables within a function (although they typically are

used with functions as shown in Fig. 15.5).

For example, the code int count = 1; // declare integer variable countint &cRef = count; // create cRef as an alias for countcRef++; // increment count (using its alias cRef)

increments variable count by using its alias cRef.

Reference variables must be initialized in their

declarations, as we show in line 9 of both Fig. 15.6 and

Fig. 15.7, and cannot be reassigned as aliases to other

variables.15


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Returning references from functions can be dangerous.

When returning a reference to a variable declared in the

called function, the variable should be declared

static within that function.

Otherwise, the reference refers to an automatic variable

that is discarded when the function terminates; such a

variable is ―undefined‖ and the program’s behavior is

unpredictable.

References to undefined variables are called dangling

references.

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It’s not uncommon for a program to invoke a function

repeatedly with the same argument value for a particular

parameter.

In such cases, the programmer can specify that such a

parameter has a default argument, i.e., a default value to

be passed to that parameter.

When a program omits an argument for a parameter

with a default argument in a function call, the compiler

rewrites the function call and inserts the default value of

that argument to be passed as an argument in the

function call.19

Default Arguments

Default arguments must be the rightmost (trailing)

arguments in a function’s parameter list.

When calling a function with two or more default

arguments, if an omitted argument is not the rightmost

argument in the argument list, then all arguments to the

right of that argument also must be omitted.

Default arguments should be specified with the first

occurrence of the function name—typically, in the

function prototype.

If the function prototype is omitted because the function

definition also serves as the prototype, then the default

arguments should be specified in the function header.20

Default Arguments …

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In C++, we begin by creating a program unit called a class tohouse a function.

A function belonging to a class is called a member function.

In a class, you provide one or more member functions thatare designed to perform the class’s tasks.

You must create an object of a class before you can get aprogram to perform the tasks the class describes.

That is one reason C++ is known as an object-orientedprogramming (OOP) language.

Messages are sent to an object. Each message is known as a

member-function call and tells a member function of the

object to perform its task.

This is often called requesting a service from an object.23

Classes and Objects

We begin with an example (Fig. 16.1) that consists of class

GradeBook (lines 8–16) that an instructor can use to

maintain student test scores, and a main function (lines 19–

23) that creates a GradeBook object.

Function main uses this object and its member function to

display a message on the screen welcoming the instructor to

the grade-book program.

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Classes and Objects …

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Function main is always called automatically when

you execute a program.

Most functions do not get called automatically.

You must call member function displayMessageexplicitly to tell it to perform its task.

The access-specifier label public: contains the

keyword public is an access specifier.

Indicates that the function is ―available to the public‖—

that is, it can be called by other functions in the program

(such as main), and by member functions of other classes

(if there are any).

Access specifiers are always followed by a colon (:).27


Each function in a program performs a task and may return a value

when it completes its task.

When you define a function, you must specify a return type to

indicate the type of the value returned by the function when it

completes its task.

Keyword void to the left of the function name displayMessageis the function’s return type.

Indicates that displayMessage will not return any data to its

calling function when it completes its task.

The name of the member function, displayMessage, follows the

return type.

By convention, function names begin with a lowercase first letter and

all subsequent words in the name begin with a capital letter.

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Empty parentheses indicate that a member function does not

require additional data to perform its task.

The first line of a function definition is commonly called the

function header.

Every function’s body is delimited by left and right braces ({

and }).

The body of a function contains statements that perform the

function’s task.

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Typically, you cannot call a member function of a class until you

create an object of that class.

First, create an object of class GradeBook called

myGradeBook.

The variable’s type is GradeBook.

The compiler does not automatically know what type GradeBookis—it’s a user-defined type.

Tell the compiler what GradeBook is by including the class

definition.

Each class you create becomes a new type that can be used to create

objects.

Call the member function displayMessage by using variable

myGradeBook followed by the dot operator (.), the function

name display-Message and an empty set of parentheses.30


Fig. 16.3 redefines class GradeBook (lines 9–18) with a

display-Message member function (lines 13–17)

that displays the course name as part of the welcome

message.

The new version of displayMessage requires a parameter

(courseName in line 13) that represents the course name to

output.

A string is actually an object of the C++ Standard Library

class string.

Defined in header file <string> and part of namespace std.

For now, you can think of string variables like variables of

other types such as int.

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Defining a Member Function with a

Parameter

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Parameter …

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Parameter …

Library function getline reads a line of text into a

string.

The function call getline( cin, nameOfCourse )reads characters (including the space characters that separate

the words in the input) from the standard input stream object

cin (i.e., the keyboard) until the newline character is

encountered, places the characters in the string variable

nameOfCourse and discards the newline character.

When you press Enter while typing program input, a newline

is inserted in the input stream.

The <string> header file must be included in the program

to use function getline.34


Parameter …

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Fundamentals of Programming - Sharifce.sharif.edu/courses/92-93/1/ce153-1/resources/root...Fundamentals of Programming Session 23 These slides have been created using Deitel’sslides