1. Chapter 3. Expressions and Interactivity

2. 3.1 The cin Object
The cin object reads information types at the keyboard.
cin is the standard input object
Notice the >> and << operators appear to point in the direction information is flowing.

3. Program 3-1 #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"; }

4. Program Output
This 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.

5. Program 3-2 // This program reads the length and width of a rectangle.
// It calculates the rectangle's area and displays
// the value on the screen.
#include <iostream.h>
void main(void) {
int Length, Width, Area;
cin >> Length;
cin >> Width;
Area = Length * Width;
cout << "The area of the rectangle is " << Area << endl; }

6. Entering Multiple Values
The cin object may be used to gather multiple values at once.

7. Program 3-3 #include <iostream.h> 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; }

8. This program calculates the area of a rectangle.
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

9. Program 3-4
// 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; }

10. Program Output
Enter an integer, a float, and a character: b [Enter]
Whole: 4
Fractional: 5.7
Letter: b

11. Reading Strings cin can read strings as well as numbers.
Strings are stored in character arrays.
char Company[12];

12. Program 3-5 #include <iostream.h> void main(void) {
char Name[21];
cout << "What is your name? ";
cin >> Name;
cout << "Good morning " << Name << endl; }

13. What is your name? Charlie [Enter] Good morning Charlie
Program Output
What is your name? Charlie [Enter]
Good morning Charlie

14. Program 3-6
// 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 names and I will\n";
cout << "reverse them.\n";
cin >> First >> Last;
cout << Last << ", " << First << endl; }

15. Program Output
Enter your first and last names and I will
reverse them.
Johnny Jones [Enter]
Jones, Johnny

16. Notes on strings:
If a character array is intended to hold strings, it must be at least one character larger than the largest string that will be stored in it.
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.
If you wish the user to enter a string that has spaces in it, you cannot use this input method.

17. 3.2 Focus on Software Engineering: Mathematical Expressions
C++ allows you to construct complex mathematical expressions using multiple operators and grouping symbols.

18. Program 3-7 #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); }

19. Program Output
This program shows the decimal value of a fraction.
Enter the numerator: 3 [Enter]
Enter the denominator: 16 [Enter]
The decimal value is

20. Table 3-1 Precedence of Arithmetic Operators (Highest to Lowest)
(unary negation) - * / % + -

21. Table 3-2 Some Expressions

22. Associativity
If two operators sharing an operand have the same precedence, they work according to their associativity, either right to left or left to right

24. Converting Algebraic Expressions to Programming Statements

25. 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

26. Program 3-8 #include <iostream.h> #include <math.h>
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 = * pow(Radius,2);
cout << "The area is " << Area; }

27. Program Output
This program calculates the area of a circle.
What is the radius of the circle? 10 [Enter]
The area is

28. 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.

29. 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.

30. 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

31. Program 3-9 #include <iostream.h> void main(void) {
short TestVar = 32767;
cout << TestVar << endl;
TestVar = TestVar + 1;
TestVar = TestVar - 1; }

32. Program Output
32767
-32768

33. Program 3-10 #include <iostream.h> void main(void) { float Test;
Test = 2.0e38 * 1000; // Should overflow Test
cout << Test << endl;
Test = 2.0e-38 / 2.0e38; }

34. 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

35. Program 3-11 #include <iostream.h> 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"; }

36. 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 books per month.

37. 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.

38. Program 3-12
// 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; }

39. Program Output 65 A

40. The Power of Constants
Constants may be given names that symbolically represent them in a program.

41. Program 3-13 #include <iostream.h> #include <math.h>
void main(void) {
const float Pi = ;
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; }

42. 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
is roughly the same as
const float PI= ;

43. Program 3-14 #include <iostream.h>
#include <math.h> // needed for pow function
#define PI  
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; }  

44. 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;

45. Table 3-8

46. Table 3-9

47. 3.8 Formatting Output
The cout object provides ways to format data as it is being displayed. This affects the way data appears on the screen.

48. Program 3-17 #include<iostream.h> void main(void) {
int Num1 = 2897, Num2 = 5, Num3 = 837, Num4 = 34, Num5 = 7,
Num6 = 1623, Num7 = 390, Num8 = 3456, Num9 = 12;
// Display the first row of numbers
cout << Num1 << " ";
cout << Num2 << " ";
cout << Num3 << endl;
// Display the second row of numbers
cout << Num4 << " ";
cout << Num5 << " ";
cout << Num6 << endl;
// Display the third row of numbers
cout << Num7 << " ";
cout << Num8 << " ";
cout << Num9 << endl; }

49. Program Output

50. Program 3-18 // This program displays three rows of numbers.
#include <iostream.h>
#include <iomanip.h>
void main(void) {
int Num1 = 2897, Num2 = 5, Num3 = 837,
Num4 = 34, Num5 = 7, Num6 = 1623,
Num7 = 390, Num8 = 3456, Num9 = 12;
// Display the first row of numbers
cout << setw(4) << Num1 << " ";
cout << setw(4) << Num2 << " ";
cout << setw(4) << Num3 << endl;

51. Program continues // Display the second row of numbers
cout << setw(4) << Num4 << " ";
cout << setw(4) << Num5 << " ";
cout << setw(4) << Num6 << endl;
// Display the third row of numbers
cout << setw(4) << Num7 << " ";
cout << setw(4) << Num8 << " ";
cout << setw(4) << Num9 << endl; }

52. Program Output

53. Program 3-19 // This program demonstrates the setw manipulator being
// used with values of various data types.
#include <iostream.h>
#include <iomanip.h>
void main(void) {
int IntValue = 3928;
float FloatValue = 91.5;
char StringValue[14] = "John J. Smith";
cout << "(" << setw(5) << IntValue << ")" << endl;
cout << "(" << setw(8) << FloatValue << ")" << endl;
cout << "(" << setw(16) << StringValue << ")" << endl; }

54. Program Output
( 3928)
( )
( John J. Smith)

55. Precision
Floating point values may be rounded to a number of significant digits, or precision, which is the total number of digits that appear before and after the decimal point.

56. Program 3-20
// This program demonstrates how setprecision rounds a // floating point value.   #include <iostream.h> #include <iomanip.h> void main(void) { float Quotient, Number1 = , Number2 = 26.91;   Quotient = Number1 / Number2; cout << Quotient << endl; cout << setprecision(5) << Quotient << endl; cout << setprecision(4) << Quotient << endl; cout << setprecision(3) << Quotient << endl; cout << setprecision(2) << Quotient << endl; cout << setprecision(1) << Quotient << endl; }

57. Program Output
4.9188
4.919
4.92
4.9 5

58. Table 3-11

59. Program 3-21
// This program asks for sales figures for 3 days. The total
// sales is calculated and displayed in a table
#include <iostream.h>
#include <iomanip.h>
void main(void) {
float Day1, Day2, Day3, Total;
cout << "Enter the sales for day 1: ";
cin >> Day1;
cout << "Enter the sales for day 2: ";
cin >> Day2;

60. Program Continues
cout << "Enter the sales for day 3: ";
cin >> Day3;
Total = Day1 + Day2 + Day3;
cout << "\nSales Figures\n";
cout << " \n";
cout << setprecision(5);
cout << "Day 1: " << setw(8) << Day1 << endl;
cout << "Day 2: " << setw(8) << Day2 << endl;
cout << "Day 3: " << setw(8) << Day3 << endl;
cout << "Total: " << setw(8) << Total << endl; }

61. Program Output
Enter the sales for day 1: [Enter]
Enter the sales for day 2: [Enter]
Enter the sales for day 3: [Enter]
Sales Figures
Day 1:
Day 2:
Day 3:
Total:

62. Program 3-22 #include <iostream.h> #include <iomanip.h>
void main(void) {
float Day1, Day2, Day3, Total;
cout << "Enter the sales for day 1: ";
cin >> Day1;
cout << "Enter the sales for day 2: ";
cin >> Day2;
cout << "Enter the sales for day 3: ";
cin >> Day3;
Total = Day1 + Day2 + Day3;

63. cout << "\nSales Figures\n"; cout << "------\n";
Program Continues
cout << "\nSales Figures\n";
cout << "------\n";
cout << setprecision(2) << setiosflags(ios::fixed);
cout << "Day 1: " << setw(8) << Day1 << endl;
cout << "Day 2: " << setw(8) << Day2 << endl;
cout << "Day 3: " << setw(8) << Day3 << endl;
cout << "Total: " << setw(8) << Total << endl; }

64. Program Output Enter the sales for day 1: 1321.87 [Enter]
Sales Figures
Day 1:
Day 2:
Day 3:
Total:

65. IOS Flags
setiosflags manipulator can be used to format output in a variety of ways, depending on which glad is specified.
setiosflags(ios::fixed) will cause all subsequent numbers to be printed in fixed point notation

66. Program 3-23
// This program asks for sales figures for 3 days. The total
// sales is calculated and displayed in a table.
#include <iostream.h>
#include <iomanip.h>
 void main(void) {
float Day1, Day2, Day3, Total;
cout << "Enter the sales for day 1: ";
cin >> Day1;
cout << "Enter the sales for day 2: ";
cin >> Day2;

67. Program continues
cout << "Enter the sales for day 3: ";
cin >> Day3;
Total = Day1 + Day2 + Day3;
cout << "\nSales Figures\n";
cout << " \n";
cout << setprecision(2)
<< setiosflags(ios::fixed | ios::showpoint);
cout << "Day 1: " << setw(8) << Day1 << endl;
cout << "Day 2: " << setw(8) << Day2 << endl;
cout << "Day 3: " << setw(8) << Day3 << endl;
cout << "Total: " << setw(8) << Total << endl; }

68. Program Output Enter the sales for day 1: 2642.00 [Enter]
Sales Figures
Day 1:
Day 2:
Day 3:
Total:

69. Table 3-12

70. 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
cout.setf(ios::fixed); //same as setiosflags(ios::fixed)

71. Program 3-24
// This program asks for sales figures for 3 days. The total
// sales is calculated and displayed in a table.
#include <iostream.h>
#include <iomanip.h>
void main(void) {
float Day1, Day2, Day3, Total;
cout << "Enter the sales for day 1: ";
cin >> Day1;
cout << "Enter the sales for day 2: ";
cin >> Day2;
cout << "Enter the sales for day 3: ";
cin >> Day3;

72. Program continues 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 << Day2 << endl;

73. Program continues cout << "Day 3: "; cout.width(8);
cout << Day3 << endl;
cout << "Total: ";
cout << Total << endl; }

74. Program Output Enter the sales for day 1: 2642.00 [Enter]
Sales Figures
Day 1:
Day 2:
Day 3:
Total:

75. Program 3-25
// This program asks for sales figures for 3 days. The total
// sales is calculated and displayed in a table.
 #include <iostream.h>
#include <iomanip.h>
 void main(void) {
float Day1, Day2, Day3, Total;
cout << "Enter the sales for day 1: ";
cin >> Day1;
cout << "Enter the sales for day 2: ";
cin >> Day2;
cout << "Enter the sales for day 3: ";
cin >> Day3;

76. cout.setf(ios::fixed | ios::showpoint);
Program continues
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 << "Day 2: " << setw(8) << Day2 << endl;
cout << "Day 3: " << setw(8) << Day3 << endl;
cout << "Total: " << setw(8) << Total << endl; }

77. Program Output Enter the sales for day 1: 2642.00 [Enter]
Sales Figures
Day 1:
Day 2:
Day 3:
Total:

78. Table 3-13

79. 3.9 Formatted Input
The cin object provides ways of controlling string and character input.

80. Program 3-26 // This program uses setw with the cin object.
#include <iostream.h>
#include <iomanip.h>
void main(void) {
char String[5];
cout << "Enter a word: ";
cin >> setw(5) >> String;
cout << "You entered " << String << endl; }

81. Program 3-27 // This program uses cin's width member function.
#include <iostream.h>
#include <iomanip.h>
void main(void) {
char String[5];
cout << "Enter a word: ";
cin.width(5);
cin >> String;
cout << "You entered " << String << endl; }

82. Program Output for Programs 3-26 and 3-27
Enter a word: Eureka [Enter]
You entered Eure

83. 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.

84. Reading a “Line” of Input
cin.getline(String, 20);

85. Program 3-28
// This program demonstrates cin's getline member function.
#include <iostream.h>
#include <iomanip.h>
void main(void) {
char String[81];
cout << "Enter a sentence: ";
cin.getline(String, 81);
cout << "You entered " << String << endl; }

86. 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.

87. Reading a character #include <iostream.h>
#include <iomanip.h>
void main(void) {
char Ch;
cout << "Type a character and press Enter: ";
cin >> Ch;
cout << "You entered " << Ch << endl; }
Program Output with Example Input
Type a character and press Enter: A [Enter]
You entered A

88. Program 3-29 #include <iostream.h> #include <iomanip.h>
void main(void) {
char Ch;
cout << "Type a character and press Enter: ";
cin >> Ch;
cout << "You entered " << Ch << endl; }
Program Output
Type a character and press Enter: A [Enter]
You entered A

89. Program 3-30 #include <iostream.h> #include <iomanip.h>
 void main(void) {
char Ch;
cout << "This program has paused. Press enter to continue.";
cin.get(Ch);
cout << "Thank you!" << endl; }
Program Output
This program has paused. Press Enter to continue. [Enter]
Thank you!

90. Program 3-31 #include <iostream.h> #include <iomanip.h>
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; }

91. Program Output Type a character and press Enter: [Enter] You entered
Its ASCII code is 10

92. 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

93. 3.10 More Mathematical Library Functions
The C++ runtime library provides several functions for performing complex mathematical operations.

94. Table 3-14

95. Table 3-14 continued

96. Table 3-14 continued

97. Program 3-32 #include <iostream.h>
#include <math.h> // For sqrt
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; }

98. 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

99. Random Numbers
rand() (from the stdlib.h library)

100. Program 3-33 // This program demonstrates random numbers.
 #include <iostream.h>
#include <stdlib.h>
void main(void) {
unsigned Seed;
cout << "Enter a seed value: ";
cin >> Seed;
srand(Seed);
cout << rand() << endl; }

101. Program Output
Enter a seed value: 5
1731
32036
21622
Program Output with Other Example Input
Enter a seed value: 16
5540
29663
9920