Lecture 25 - C++ IO&Classes - 06

7/29/2019 Lecture 25 - C++ IO&Classes - 06

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Engineering H192 - Computer Programming

Gateway Engineering Education Coalition Lect 25 P. 1Winter Quarter

C++: I/O and Classes

Lecture 25


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Keyboard & Screen I/O in C++

It is perfectly valid to use the same I/O statements inC++ as in C -- The very same pr int f, scanf, and otherstdio.hfunctions that have been used until now.

However, C++ provides an alternative with the newstream input/output features. The header file isnamed iostream and the stream I/O capabilities areaccessible when you use the pre-processordeclaration:

#include // No .h on std headersusing namespace std; // To avo id th ings like

// s td ::cou t and s td ::c in


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Several new I/O objects available when you

include the iostream header file. Two important

ones are:

cin // Used for keyboard input (std::cin)

cout // Used for screen output (std::cout)

Both c inand coutcan be combined with other

member functions for a wide variety of special I/O

capabilities in program applications.


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Since cin and cout are C++ objects, they aresomewhat "intelligent":

They do not require the usual format strings

and conversion specifications. They do automatically know what data types

are involved.

They do not need the address operator, &.

They do require the use of the streamextraction ( >> ) and insertion (


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Example using cin and cout#include using namespace std; // replace every cin and cout

// with std::cin and std::cout

// without this line

int main ( )

{int a, b; float k; charname[30];

cout> name ;

cout > a >> b >> k ;

cout


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Example Program Output

Enter your name

Rick

Enter two integers and a float

20 30 45.67

Thank you, Rick, you entered

20, 30, and 45.67


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Input Stream Object Member Functions

cin.getline(array_name, max_size);

Example:charname[40] ;

cin.getline(name, 40); // gets a string from

// keyboard and assigns

// to name


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Classes in C++

Classes enable a C++ program to model objects

that have:

attributes (represented by data members).

behaviors or operations (represented bymember funct ions) .

Types containing data membersand member

funct ionprototypes are normally defined in a C++program by using the keyword class.


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Classes in C++ A class definition begins with the keyword class.

The body of the class is contained within a set of

braces, { } ; (notice the semi-colon).

Within the body, the keywords private:and

publ ic :specify the access level of the membersof the class. Classes default to private.

Usually, the data members of a class are declared

in the private:section of the class and the

member functions are in publ ic :section. Private members of the class are normally not

accessible outside the class, i.e., the information

is hidden from "clients" outside the class.


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Classes in C++

A member function prototype which has the verysame name as the name of the class may bespecified and is called the constructor function.

The definition of each member function is "tied"back to the class by using the binary scoperesolution operator ( :: ).

The operators used to access class members areidentical to the operators used to accessstructure members, e.g., the dot operator (.).


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Classes Example

#include #include // This is the same as string.h in C

using namespace std;

class Numbers // Class definition

{

public: // Can be accessed by a "client".Numbers ( ); // Class "constructor"

void display ( ) ;

void update ( ) ;

private: // Cannot be accessed by "client"

charname[30] ;int a ;

float b ;

} ;


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Classes Example (continued)

Numbers::Numbers ( ) // Constructor member function{

strcpy(name, "Unknown");

a = 0;

b = 0.0;}

void Numbers::display ( ) // Member function

{

cout


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void Numbers::update ( ) // Member function

{

cout


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int main ( ) // Main program

{

Numbers no1, no2 ; // Create two objects of

// the class "Numbers"

no1.update ( ) ; // Update the values of

// the data members

no1.display ( ) ; // Display the current

no2.display ( ) ; // values of the objects

}


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Example Program Output

r1tel (~) freuler 53> example.out

The name is Rick FreulerThe numbers are 9876 and 5.4321

The name is Unknown

The numbers are 0 and 0


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More Detailed Classes Example

#include #include


class Numbers // Class definition

{

public:Numbers (char[ ] = "Unknown", int = 0, float = 0.0);

void display ( );

void update ( ) ;

private:

charname[30];int a;

float b;

} ;


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More Detailed Classes Example (continued)

Numbers::Numbers (charnm[ ], int j, float k )

{

strcpy(name, nm);

a = j ;

b = k ;

}

void Numbers::update ( )

{

cout > b ;

}


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More Detailed Classes Example (continued)

void Numbers::display( ){

cout


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More Detailed Example Program Output

r1rhl (~) freuler 76> example.out

The name is Unknown

The numbers are 0 and 0

The name is John Demel

The numbers are 12345 and 678.9


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Some Help for G23

Use

#include


When using these, use the following compile

command

g++ o g23.out g23.cpp


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Some Guidance on G23

class Complex

{ private:

float fReal;

float fImag;

public:

Complex(); // Constructor function prototype

void mult(_______); // rest of function prototypes};

What goes here?


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Gateway Engineering Education Coalition Lect 25 P. 22

http://www.google.com.ph/search?q=introduction+to+c%2B%2B.ppt&ie=utf-8&oe=utf-

8&aq=t&rls=org.mozilla:en-US:official&client=firefox-

a#q=introduction+to+c%2B%2B.ppt&hl=fil&client=firefox-a&hs=uIl&rls=org.mozilla:en-

US:official&prmd=imvns&ei=IIgjUMOqMIOPmQWPxYDwDA&start=10&sa=N&bav=on.2,or.r_gc.r_pw.r_

qf.&fp=bc18a79a89ac87b8&biw=1291&bih=693

Hints on Multiplying Complex Numbers

For the function

void Complex::mult (Complex imag_n)

{

// you need to use the distributive property!

// (a + b*i)*(c + d*i) = (a*c b*d) + (b*c + a*d)*i

// real part + iimag part

}

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Lecture 25 - C++ IO&Classes - 06