Chapter 3: Expressions & Interactivity. Resource: Starting Out with C++, Third Edition, Tony Gaddis 3.1The cin Object The cin object reads information

Chapter 3: Expressions & Interactivity

Resource: Starting Out with C++, Third Edition, Tony Gaddis

3.1 The cin Object

• The cin object reads information typed from the keyboard.

• cin is the standard input object.• The cin object causes a program to wait

until information is typed at the keyboard and the [Enter] key is pressed.

• cin automatically converts the information read from the keyboard to the data type of the variable used to store it.

• You must include the iostream.h file in any program that uses cin.


3-1 Program#include <iostream.h>

void main(void)

{

int length, width, area;

cout << "This program calculates the area of a rectangle.\n";

cout << "What is the length of the rectangle? ";

cin >> length;

cout << "What is the width of the rectangle? ";

cin >> width;

area = length * width;

cout << "The area of the rectangle is " << area << ".\n";

}


3-1 Program OutputThis program calculates the area of a rectangle.

What is the length of the rectangle? 10 [Enter]

What is the width of the rectangle? 20 [Enter]

The area of the rectangle is 200.


>> and << Operators

• Notice the >> and << operators appear to point in the direction information is flowing.

• The >> operator indicates information flows from cin to a variable.

• The << operator shows that information flows from a variable (or constant) to cout.


3.1 The cin Object Continued

• cin is smart enough to know a value like 10.7 cannot be stored in an integer variable.

• If the user enters a floating point value into an integer variable, the part of the number after the decimal point is thrown away.

• When part of a value is discarded, it is truncated. cin truncates floating point numbers that are to be stored in integer variables.


Users of Your Programs

• Always explain to the user what the program is or what information is needed.

• Always be courteous and prompt the user to enter exactly what the program needs.

• Users do not want to see your source code.


Entering Multiple Values

• The cin object may be used to gather multiple values at once.

• cin will read multiple values of different data types.



void main(void){int length, width, area;cout << "This program calculates the area of a rectangle.\n";cout << "Enter the length and width of the rectangle separated by a space. \n";cin >> length >> width;area = length * width;cout << "The area of the rectangle is " << area << endl;

}


3-3 Program Output

This program calculates the area of a rectangle.

Enter the length and width of the rectangle separated by a space.

10 20 [Enter]

The area of the rectangle is 200


3-4 Program//This program demonstrates how cin can read multiple //values of different data types.#include <iostream.h>

void main(void){

int whole;float fractional;char letter;

cout << "Enter an integer, a float, and a character: ";cin >> whole >> fractional >> letter;cout << "whole: " << whole << endl;cout << "fractional: " << fractional << endl;cout << "letter: " << letter << endl;

}


3-4 Program Output

Enter an integer, a float, and a character: 4 5.7 b [Enter]

whole: 4

fractional: 5.7

letter: b


Reading Strings

• cin can read strings, as well as, numbers.

• In C++, C-strings are commonly stored in character arrays.

• An array is like a group of variables with a single name, located together in memory.


Character Array

• An example of a character array declaration: char company[12];

• The number inside the brackets indicates the size of the array.

• The name of the array is company, and it is large enough to hold 12 characters.

• Remember that C-strings have the null terminator at the end, so this array is large enough to hold a C-string that is 11 characters long.


3-5 Program//This program shows how cin may //be used to read a string into a//character array#include <iostream.h>#include<string>

void main(void){string name;cout << "What is your name? ";cin >> name;cout << "Good morning " << name << endl;

}


3-5 Program Output

What is your name? Charlie [Enter]

Good morning Charlie


char name[21];

• The name of the array is name and it is large enough to hold 21 characters.

• The null terminator at the end of a C-string is a character, so the longest string that may be stored in this array is 20 characters.

• The cin object will let the user enter a string larger than the array can hold. If this happens, the string will overflow the array’s boundaries and destroy other information in memory.


3-6 Program

//This program reads two strings into //two character arrays.#include <iostream.h>

void main(void){char first[16], last[16];cout << "Enter your first and last name and I will\n";cout << "reverse them.\n"; cin >> first >> last;cout << last << ", " << first << endl;

}


3-6 Program Output

Enter your first and last names and I will

reverse them.

Johnny Jones [Enter]

Jones, Johnny


Notes on Strings

• If you wish the user to enter a string that has spaces in it, you cannot use this input method.


3.2 Mathematical Expressions

• C++ allows you to construct complex mathematical expressions using multiple operators and grouping symbols.

• Mathematical expressions are evaluated from left to right.

• When two operators share an operand, the operator with the highest precedence works first.

• Multiplication and division have higher precedence than addition and subtraction.


Expression

• An expression is a programming statement that has a value.

• Usually, an expression consists of an operator and its operands.

• Sum = 21 + 3: Since 21 + 3 has a value, it is an expression. Its value, 24, is stored in the variable sum.

• Expressions do not have to be in the form of mathematical operations. number = 3; 3 is an expression.


3-7 Program// This program asks the user to enter the numerator// and denominator of a fraction and it displays the// decimal value#include <iostream.h>

void main(void){

float numerator, denominator;

cout << "This program shows the decimal value of ";cout << "a fraction.\n";

cout << “Enter the numerator: “;cin >> numerator;cout << “Enter the denominator: “;cin >> denominator;

cout << “The decimal value is “; cout << (numerator / denominator);}


3-7 Program Output with Example Input

This program shows the decimal value of a fraction.

Enter the numerator: 3 [Enter]

Enter the denominator: 6 [Enter]

The decimal value is 0.1875


Precedence of Arithmetic Operators (Highest to Lowest)

(unary negation) -* / %+ -

Table 3-2 Some Expressions with their Values

Expression Value 5 + 2 * 4 13 10 / 2 - 3 2 8 + 12 * 2 - 4 28 4 + 17 % 2 - 1 4 6 - 3 * 2 + 7 - 1 6


Associativity

• If two operators sharing an operand have the same precedence, they work according to their associativity.

• Associativity is either right to left or left to right.

• It is the order in which an operator works with its operands.

• The associativity of the division operator is left to right, so it divides the operand on its left by the operand on its right.

Operator Associativity (unary negation) - Right to left * / % Left to right + - Left to right

Table 3-3 Associatively of Arithmetic Operators

Grouping with Parentheses: Parts of a mathematical expression may be grouped with parentheses to force some operations to be performed before others.

Converting Algebraic Expressions to Programming

Statements

Algebraic Expression

Operation C++ Equivalent

6B 6 times B 6 * B (3)(12) 3 times 12 3 * 12 4xy 4 times x times y 4 * x * y

In algebra it is not always necessary to use an operator for multiplication. However, C++ requires an operator for any mathematical operation. The above table shows some algebraic expressions that perform multiplication and the equivalent C++ expression.


No Exponents Please!

• C++ does not have an exponent operator.

• Use the pow() library function to raise a number to a power.

• Will need #include <math.h> for pow() function.

area = pow(4,2) // will store 42 in area


pow function

• Must include math.h header file.• The variable used to store pow’s return

value should be declared as a double or a float.

• The pow function is designed to return a double. Remember that a double value will fit in a float variable if the value is small enough.

• If the arguments of the pow function are large enough to cause pow to produce a value outside the range of a float, a double variable should be used to store its return value.


3-8 Program// This program calculates the area of a circle.// The formula for the area of a circle is Pi times// the radius squared. Pi is 3.14159.#include <iostream.h>#include <math.h> // needed for the pow function

void main(void){

double area, radius;cout << "This program calculates the area of a circle.\n";cout << "What is the radius of the circle? ";cin >> radius;area = 3.14159 * pow(radius,2);cout << "The area is " << area;

}



This program calculates the area of a circle.

What is the radius of the circle? 10[Enter]

The area is 314.159


3.3 When you Mix Apples and Oranges: Type Coercion

• When an operator’s operands are of different data types, C++ will automatically convert them to the same data type.


Type Coercion Rules:

• Rule 1: Chars, shorts, and unsigned shorts are automatically promoted to int.

• Rule 2: When an operator works with two values of different data types, the lower-ranking value is promoted to the type of the higher-ranking value.

• Rule 3: When the final value of an expression is assigned to a variable, it will be converted to the data type of the variable.


3.4 Overflow and Underflow

• When a variable is assigned a value that is too large or too small in range for that variable’s data type, the variable overflows or underflows.

• Overflow - when a variable is assigned a number that is too large for its data type

• Underflow - when a variable is assigned a number that is too small for its data type


3-9 Program

// This program demonstrates integer underflow and

// overflow

#include <iostream.h>

void main(void)

{

short testVar = 32767;

cout << testVar << endl;

testVar = testVar + 1;


testVar = testVar - 1;


}


3-9 Program Output

32767

-32768

32767


3-10 Program

// This program can be used to see how your system

// handles floating point overflow and underflow.


void main(void)

{

float test;

test = 2.0e38 * 1000; // Should overflow test

cout << test << endl;

test = 2.0e-38 / 2.0e38;

cout << test << endl;

}


3.5 The Typecast Operator

• The typecast operator allows you to perform manual data type conversion.

Val = int(number); //If number is a floating

//point variable, it will be

//truncated to an integer and

//stored in the variable Val


3-11 Program


void main(void){

int months, books;float perMonth;cout << "How many books do you plan to read? ";cin >> books;cout << "How many months will it take you to read them? ";cin >> months;perMonth = float(books) / months;cout << "That is " << perMonth << " books per month.\n";

}


3-11 Program Output

How many books do you plan to read? 30 [Enter]

How many months will it take you to read them? 7 [Enter]

That is 4.285714 books per month.


Typecast Warnings

• In Program 3-11, the following statement would still have resulted in integer division:

perMonth = float(books / months);

• Because the division is performed first and the result is cast to a float.


3-12 Program

//This program uses a typecast operator to//print a character from a number. #include <iostream.h>

void main(void){int number = 65;cout << number << endl;cout << char(number) << endl;

}


3-12 Program Output

65

A


3.6 The Power of Constants

• Constants may be given names that symbolically represent them in a program.


3-13 Program// This program calculates the area of a circle.#include <iostream.h>#include <math.h>

void main(void){

const float pi = 3.14159;double area, radius;cout << "This program calculates the area of a circle.\n";cout << "What is the radius of the circle? ";cin >> radius;area = pi * pow(radius,2);cout << "The area is " << area;

}


The #define Directive

• The older C-style method of creating named constants is with the #define directive, although it is preferable to use the const modifier.

#define PI 3.14159

• is roughly the same as

const float PI=3.14159;


3-14 Program

#include <iostream.h>#include <math.h> // needed for pow function#define PI 3.14159

void main(void){

double area, radius;cout << "This program calculates the area of a circle.\n";cout << "What is the radius of the circle? ";cin >> radius;area = PI * pow(radius, 2);cout << "The area is " << area;

}


3.7 Multiple Assignment and Combined Assignment

• Multiple assignment means to assign the same value to several variables with one statement.

A = B = C = D = 12;

Store1 = Store2 = Store3 = BegInv;


3-15 Program// The program tracks the inventory of three widget stores// that opened at the same time. Each store started with the// same number of widgets in inventory. By subtracting the// number of widgets each store has sold from its inventory,// the current inventory can be calculated.


void main(void){

int begInv, sold, store1, store2, store3;

cout << “One week ago, 3 new widget stores opened\n";cout << “at the same time with the same beginning\n";cout << “inventory. What was the beginning inventory? ";cin >> begInv;store1 = store2 = store3 = begInv;


3-15 Program Continued

cout << "How many widgets has store 1 sold? ";cin >> sold;store1 = store1 – sold; //Subtract sold from store1

cout << "How many widgets has store 2 sold? ";cin >> sold;store2 = store2 – sold; //Subtract sold from store2cout << "How many widgets has store 3 sold? ";cin >> sold;store3 = store3 – sold; //Subtract sold from store 3cout << "Store1: " << store1 << endl;cout << "Store2: " << store2 << endl;cout << "Store3: " << store3 << endl;

}



One week ago, 3 new widget stores opened

at the same time with the same beginning

inventory. What was the beginning inventory? 100 [Enter]

How many widgets has store 1 sold? 25 [Enter]



The current inventory of each store:

Store 1: 75

Store 2: 85

Store 3: 55

Table 3-8

Statement What I t Does Value of x after the

Statement

x = x + 4; Adds 4 to x 10

x = x - 3 ; Subtracts 3 from x 3

x = x * 10; Multiplies x by 10 60

x = x / 2 ; Divides x by 2 3

x = x % 4 Makes x the remainder of x / 4 2

Table 3-9

Operator Example Usage Equivalent To += x += 5; x = x + 5; -= y -= 2; y = y - 2; *= z += 10; z = z + 10; /= a /= b; a = a / b;

%= c %= 3; c = c % 3;


3-16 Program// The program tracks the inventory of three widget stores

// that opened at the same time. Each store started with the

// same number of widgets in inventory. By subtracting the

// number of widgets each store has sold from its inventory,

// the current inventory can be calculated.


void main(void)

{

int begInv, sold, store1, store2, store3;

cout << “One week ago, 3 new widget stores opened\n";

cout << “at the same time with the same beginning\n";

cout << “inventory. What was the beginning inventory? ";

cin >> begInv;

store1 = store2 = store3 = begInv;



cout << "How many widgets has store 1 sold? ";cin >> sold;store1 -= sold; //Subtract sold from store1

cout << "How many widgets has store 2 sold? ";cin >> sold;store2 -= sold; //Subtract sold from store2cout << "How many widgets has store 3 sold? ";cin >> sold;store3 -= sold; //Subtract sold from store 3cout << "Store1: " << store1 << endl;cout << "Store2: " << store2 << endl;cout << "Store3: " << store3 << endl;

}



One week ago, 3 new widget stores opened

at the same time with the same beginning

inventory. What was the beginning inventory? 100 [Enter]




The current inventory of each store:

Store 1: 75

Store 2: 85

Store 3: 55

Table 3-12

Format Flag Description

ios::left Causes the field to be left-justified with padding spaces printed tothe right.

ios::right Causes the field to be right-justified with padding spaces printed tothe left.

ios::fixed Causes all subsequent numbers to be displayed in fixed pointnotation.

ios::scientific Causes all subsequent numbers to be displayed in scientific notation.

ios::dec Causes all subsequent integers to be displayed in decimal format.

ios::hex Causes all subsequent integers to be displayed in hexadecimalformat.

ios::oct Causes all subsequent integers to be displayed in octal format.

ios::showpoint Forces the decimal point and trailing zeroes to be displayed.

ios::showpos Causes a + sign to be displayed in front of positive numbers.

ios::uppercase Causes the E in scientific notation numbers, and the X inhexadecimal numbers to be displayed in uppercase.


Formatting Output with Member Functions

cout.width(5); //calls the width member

// function, same as

// setw(5)

cout.precision(2); //sets precision to

// 2 significant

// digits

// The next statement works like

// setiosflags(ios::fixed)

cout.setf(ios::fixed);


3-24 Program// This program asks for sales figures for 3 days. The

// total sales is calculated and displayed in a table.


#include <iomanip.h>

void main(void)

{

float day1, day2, day3, total;

cout << "Enter the sales for day 1: ";

cin >> day1;


cin >> day2;


cin >> day3;



total = day1 + day2 + day3; cout.precision(2); cout.setf(ios::fixed | ios::showpoint);cout << "\nSales Figures\n";cout << "-------------\n";cout << “Day 1: ";cout.width(8);cout << day1 << endl;cout << “Day 2: ";cout.width(8);cout << day2 << endl;


cout << “Day 3: ";

cout.width(8);

cout << day3 << endl;

cout << "Total: ";

cout.width(8);

cout << total << endl;

}



3-24 Program Output

Enter the sales for day 1: 2642.00 [Enter]



Sales Figures

-------------

Day 1: 2642.00

Day 2: 1837.20

Day 3: 1963.00

Total: 6442.20


3-25 Program

// This program asks for sales figures for 3 days. The

// total sales is calculated and displayed in a table.



void main(void)

{

float day1, day2, day3, total;


cin >> day1;


cin >> day2;


cin >> day3;



total = day1 + day2 + day3;

cout.precision(2);

cout.setf(ios::fixed | ios::showpoint);

cout << "\nSales Figures\n";

cout << "-------------\n";

cout << “Day 1: " << setw(8) << day1 << endl;



cout << "Total: " << setw(8) << total << endl;

return 0;

}


3-25 Program Output




Sales Figures

-------------

Day 1: 2642.00

Day 2: 1837.20

Day 3: 1963.00

Total: 6442.20

Table 3-13

Member Function Description cout.width Sets the display field width. cout.precision Sets the precision of floating point

numbers. cout.setf Sets the specified format flags. cout.unsetf Disables, or turns off, the specified

format flags.


3.9 Formatted Input

• The cin object provides ways of controlling string and character input.


3-26 Program

//This program uses setw with the cin object.



void main(void)

{

char word[5];

cout << "Enter a word: ";

cin >> setw(5) >> word;

cout << "You entered " << word << endl;

}


3-27 Program

//This program uses cin's width member function. #include <iostream.h>#include <iomanip.h>

void main(void){ char word[5]; cout << "Enter a word: "; cin.width(5); cin >> word; cout << "You entered " << word << endl;}


3-26 and 3-287Program Output

Enter a word: Eureka [Enter]

You entered Eure


Important points about the way cin handles field widths:

• The field width only pertains to the very next item entered by the user.

• cin stops reading input when it encounters a whitespace character. Whitespace characters include the [Enter] key, space, and tab.


Reading a “Line” of Input

cin.getline(line, 20);


3-28 Program

//This program demonstrates cin's getline member

//function.



void main(void)

{

char sentence[81];

cout << "Enter a sentence: ";

cin.getline(sentence, 81);

cout << "You entered " << sentence << endl;

}


3-28 Program Output

Enter a sentence: To be, or not to be, that is the question. [Enter]

You entered To be, or not to be, that is the question.



void main(void){char ch;

cout << "Type a character and press Enter: ";cin >> ch;cout << "You entered " << ch << endl;

}

Program Output with Example InputType a character and press Enter: A [Enter]

You entered A



void main(void){

char ch;

cout << "This program has paused. Press enter to continue.";cin.get(ch);cout << "Thank you!" << endl;

}Program OutputThis program has paused. Press Enter to continue.

[Enter]Thank you!


3-31 Program


void main(void)

{

char ch;

cout << "Type a character and press Enter: ";

cin.get(ch);

cout << "You entered " << ch << endl;

cout << "Its ASCII code is " << int(ch) << endl;

}


3-31 Program Output

Type a character and press Enter: [Enter]

You entered

Its ASCII code is 10


Mixing cin >> and cin.get

• Mixing cin.get with cin >> can cause an annoying and hard-to-find problem.

• Pressing the [Enter] key after inputting a number will cause the newline character to be stored in the keyboard buffer. To avoid this, use cin.ignore.

• cin.ignore(20,’\n’); will skip the next 20 chars in the input buffer or until a newline is encountered, whichever comes first.

• cin.ignore(); will skip the very next character in the input buffer.


3.10 More About Object-Oriented Programming

• A member function is a procedure, written in C++ code, that is part of an object. A member function causes the object it is a member of to perform an action.

• In this chapter, we have used width, precision, setf, and unsetf for the cout object.

• In this chapter we have used width, getline, get, and ignore for the cin object.


3.11 More Mathematical Library Functions

• The C++ runtime library provides several functions for performing complex mathematical operations.

• In this chapter we have used width, precision, setf, and unsetf for the cout object.

• In this chapter we have used width, getline, get, and ignore for the cin object.

Table 3-14

a b s Example Usage: y = a b s (x ) ;

Description Returns the absolute value of the argument. The argument and the return value are integers.

c o s Example Usage: y = c o s (x ) ;

Description Returns the cosine of the argument. The argument should be an angle expressed in radians. The return type and the argument are doubles.

e x p Example Usage: y = e x p (x );

Description Computes the exponential function of the argument, which is x . The return type and the argument are doubles.

Table 3-14 Continued

fm o d Example Usage: y = fm o d (x , z );

Description Returns, as a double, the remainder of the first argument divided by the second argument. Works like the modulus operator, but the arguments are doubles. (The modulus operator only works with integers.) Take care not to pass zero as the second argument. Doing so would cause division by zero.

lo g Example Usage: y = lo g (x );

Description Returns the natural logarithm of the argument. The return type and the argument are doubles.

lo g 1 0 Example Usage: y = lo g 1 0 (x );

Description Returns the base-10 logarithm of the argument. The return type and the argument are doubles.

Table 3-14 Continueds in Example Usage:

y = s in (x );

Description Returns the sine of the argument. The argument should be an angle expressed in radians. The return type and the argument are doubles.

sq rt Example Usage:

y = sq rt(x );

Description Returns the square root of the argument. The return type and argument are doubles.

tan Example Usage:

y = ta n (x );

Description Returns the tangent of the argument. The argument should be an angle expressed in radians. The return type and the argument are doubles.


3-32 Program

// This program asks for the lengths of the 2 sides of a right // triangle. The length of the hypotenuse is then calculated// and displayed.#include <iostream.h>#include <math.h> // For sqrt and pow

void main(void){

float a, b, c;

cout << "Enter the length of side A: ";cin >> a;cout << "Enter the length of side B: ";cin >> b;c = sqrt(pow(a, 2.0) + pow(b, 2.0));cout.precision(2);cout << "The length of the hypotenuse is ";cout << c << endl;

}


3-32 Program Output

Enter the length of side A: 5.0 [Enter]

Enter the length of side B: 12.0 [Enter]

The length of the hypotenuse is 13


Random numbers

rand() (from the cstdlib library)


3-33 Program

// This program demonstrates random numbers.#include <iostream.h>#include <stdlib.h>using namespace std;

void main(void){

unsigned seed;cout << "Enter a seed value: ";cin >> seed;srand(seed);cout << rand() << endl;cout << rand() << endl;cout << rand() << endl;

}


3-33 Program Output

Enter a seed value: 5

1731

32036

21622Program Output with Other Example Input

Enter a seed value: 16

5540

29663

9920


3.13 Introduction to Simple File Input and Output

• What is a File? A file is a collection on information, usually stored on a computer’s disk. Information can be saved to files and then later reused.


The Process of Using a File

• Using a file in a program is a simple three-step process:1. The file must be opened. If the

file does not yet exits, opening it means creating it.

2. Information is then saved to the file, read from the file, or both.

3. When the program is finished using the file, the file must be closed.

Figure 3-8

Figure 3-9


Setting Up a Program for File Input/Output (I/O)

• Before file I/O can be performed, a C++ program must be set up properly.

• File access requires the inclusion of the fstream.h header file.

Table 3-16

File Type Default Open Mode ofstream The file is opened for output only. Information may be

written to the file, but not read from the file.

ifstream The file is opened for input only. Information may be read from the file, but not written to it.

fstream The file is opened for input and output. Information may be written to the file or read from it.


Opening a File

• Before data can be written to or read from a file, the file must be opened.

ifstream inputFile;

inputFile.open(“customer.dat”);


Closing a File

• A file should be closed when a program is finished using it.

outputFile.close();


Writing Information to a File

• The stream insertion operator (<<) may be used to write information to a file.

outputFile << “I love C++ programming !”

outputFile << “Price: “ << price;


3-36 Program// This program uses the << operator to write information to a// file.#include <iostream.h>#include <fstream.h>

void main(void){

ofstream outputFile;

outputFile.open("demofile.txt");cout << "Now writing information to the file.\n";

// Write 4 great names to the fileoutputFile << "Bach\n";outputFile << "Beethoven\n";outputFile << "Mozart\n";outputFile << "Schubert\n";



// Close the fileoutputFile.close();cout << "Done.\n";

}

Program Screen Output

Now writing information to the file.Done.

Program Output to File demofile.txt

BachBeethovenMozartSchubert


Reading Information from a File

• The stream extraction operator (>>) may be used to read information from a file.

inFile >> name;


3-37 Program// This program uses the >> operator to read information from a// file.#include <iostream.h>#include <fstream.h>

void main(void){

ifstream inFile;int length, width, area;

inFile.open("dimensions.txt");cout << "Reading dimensions of 5 rectangles from the file.\n\n";

// Process rectangle 1inFile >> length;inFile >> width;area = length * width;cout << "Area of rectangle 1: " << area << endl;



Program 3-37 Continued// Process rectangle 3inFile >> length;inFile >> width;area = length * width;cout << "Area of rectangle 3: " << area << endl;



// Close the fileinFile.close();cout << "\nDone.\n";

}


3-37 Program

Before Program 3-37 is executed, the file dimensions.txt must be created with a text editor (such as Windows Notepad). Here is an example of the file's contents:

10 25 718 96 208 3


3-37 Program Output

Reading dimensions of 5 rectangles from the file.

Area of rectangle 1: 20Area of rectangle 2: 35Area of rectangle 3: 162Area of rectangle 4: 120Area of rectangle 5: 24

Done.

Documents

Chapter 3: Expressions & Interactivity. Resource: Starting Out with C++, Third Edition, Tony Gaddis 3.1The cin Object The cin object reads information