1. CS102 Introduction to Computer Programming
Week 3
Chapter 3
Expressions and Interactivity

2. Chapter 3 Expressions and Interactivity
The cin object
Mathematical Expressions
Automatic conversion and promotion
Overflow and underflow
The typecast operator
The power of constants
Multiple assignments
Combined assignment operators
Formatting output with stream manipulators
Formatted input
More mathematical library functions

4. Concept - The cin object reads information typed at the keyboard
cin is the standard input object
Causes the program to wait until information is typed at the keyboard and the enter key is pressed
Automatically converts the data read to the type of the variable used to store it
Truncates floating point numbers that are to be stored in integer variables
Notice the >> and << operators appear to point in the direction information is flowing.
Concept - The cin object reads information typed at the keyboard

5. Program 3-1 This program will calculate the area of any rectangle
#include <iostream>
using namespace std;
void main()‏ {
int Length, Width, Area;
cout <<"This program calculates the";
cout <<" area of a rectangle.\n";
cout <<"What is the length of the ";
cout <<" rectangle? ";
cin >>Length;
cout <<"What is the width of the";
cin>>Width;
Area = Length * Width;
cout <<"The area of the rectangle is "
cout << Area << ".\n"; }
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.

6. 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>
using namespace std;
void main()‏ {
int Length, Width, Area;
cin >> Length;
cin >> Width;
Area = Length * Width;
cout << "The area of the rectangle is " << Area << endl; }
This program does not let the user know what is needed as input.
Program Output
10 [Enter]
20 [Enter]
The area of the rectangle is 200.

7. Concept - The cin object can gather multiple values at once
Multiple values are separated by spaces
The Variables are assigned values in the order they are entered.
cin can read character strings into a properly defined variable
If the input string is too large, adjacent memory can be corrupted
Don't forget to leave room for the null character
The string can not contain spaces
Concept - The cin object can gather multiple values at once

8. Program 3-3 #include <iostream> using namespace std;
void main()‏ {
int Length, Width, Area;
cout <<"This program calculates";
cout <<" the area of a rectangle.\n";
cout <<"Enter the length and width";
cout <<" of the rectangle separated";
cout <<" by a space. \n";
cin >> Length >> Width;
Area = Length * Width;
cout <<"The area of the rectangle is ";
cout << Area << endl; }
This program accepts multiple entries on one line
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 or 3-3 version 4
/* This program demonstrates how cin can read multiple values of different data types. */
 #include <iostream>
 using namespace std;
void main()‏ {
int Whole;
float Fractional;
char Letter;
cout << "Enter an integer, a float, ";
cout << "and a character: ";
cin >> Whole >> Fractional >> Letter;
cout << "Whole: " << Whole << endl;
cout << "Fractional: " << Fractional << endl;
cout << "Letter: " << Letter << endl; }
Values of different data types can be
entered on the same line. They must be
entered in the correct order
Program Output
Enter an integer, a float,
and a character: b [Enter]
Whole: 4
Fractional: 5.7
Letter: b

10. Program 3-5 or 3-4 version 4
// This program demonstrates how cin can read a string into a character array. */
#include <iostream>
using namespace std;
void main()‏ {
char Name[21];
cout << "What is your name? ";
cin >> Name;
cout << "Good morning ";
cout << Name << endl; }
cin can read strings as well as numbers. Strings are stored in character arrays.
Program Output
What is your name? Charlie [Enter]
Good morning Charlie

11. Program 3-6 or 3-5 version 4 // This program reads two strings
Note that a space is used to separate the two inputs. If you want to read in a string with embedded spaces you can not use the cin command
// This program reads two strings
// into two character arrays.
#include <iostream>
using namespace std;
void main()‏ {
char First[16], Last[16];
  cout << "Enter your first and last";
cout << " names and I will\n";
cout << "reverse them.\n";
cin >> First >> Last;
cout << Last << ", " << First;
cout <<endl; }
Program Output
Enter your first and last
names and I will
reverse them.
Johnny Jones [Enter]
Jones, Johnny

12. 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.

13. Check point 3.1
3.1 What header file must be included in programs using cin?
3.2 What type of variable is used to hold a C-string?
3.3 Write a declaration statement for a character array named customer. It should be large enough to hold 52 characters in length.
3.4 T or F: cin requires the user to press the [Enter] key when finished entering data
3.5 Assume value is an integer variable. If the user enters 3.14 in response to the following programming statement, What will be stored in value
cin >> value;
3.14 3
Nothing, an error message is displayed
<iostream>
char
char customer[53];

14. Mathematical Expressions
A mathematical expression is a programming statement that has a value
Consists of operators and their operands
operands can be constants or variables
Can be used by the cout object to display the value of the expression.
cout << (Operand1 operator Operand2);
Concept - C++ allows you to construct complex mathematical expressions using multiple operators and grouping symbols

15. Program 3-7 or 3-6 version 4
Mathematical expressions can be used in cout statements.
Note the inputs are integers but they are converted to floats for storage
/* This program asks the user top enter the numerator and denominator of a fraction and it displays the decimal value*/
using namespace std;
void main()‏ {
float Numerator, Denominator;
cout << "This program shows the ";
cout << "decimal value of a fraction.\n";
cout << "Enter the numerator: ";
cin >> Numerator;
cout << "Enter the denominator: ";
cin >> Denominator;
cout << "The decimal value is ";
cout << (Numerator / Denominator); }
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
0.1875

16. Mathematical expressions are evaluated left to right
Precedence
If two operators share an operand the one with the highest precedence works first
highest - (Unary negation)‏
* / %
Lowest + -
Example 6 * = 39 (not 24)‏
Example / 3 = 7 (not 5 )‏
Mathematical expressions are evaluated left to right

17. Associativity Associativity is either left to right or right to left
If two operators sharing an operand have the same precedence, they work according to their Associativity.
Right to left - (Unary negation)‏
left to right * / %
left to right + -
Associativity is the order in which an operator works with its operands

18. Grouping With Parentheses
Parentheses are used to force some operations to be performed before others
examples:
(5+2)*4 = 28
10 / (5-3) = 5
( ) % 2 -1 = 0

19. No Exponents Please
Include the following file in your program to deal with exponents:
#include <math>
Use the pow function to raise a value (x) to the power (y) (x and y may be int or float)‏
example: the area of a circle is (radius2)‏
Area = 3.14 * pow(radius,2);
The pow function returns a double
Concept - C++ does not have an operator to raise a number to a power. A library function must be used

20. Program 3-8 or 3-7 version 4
/*This program calculates the area of a circle. The formula for the radius of a circle is Pi times the radius squared Pi is */
#include <iostream>
#include <math.h>
using namespace std;void main()‏ {
double Area, Radius;
cout << "This program calculates the ";
cout << " area of a circle.\n";
cout << "What is the radius of ";
cout << "the circle? ";
cin >> Radius;
Area = * pow(Radius,2);
cout << "The area is " << Area; }
This program uses the pow function to find the area of a circle
Program Output
This program calculates the
area of a circle.
What is the radius of the
circle?
10 [Enter]
The area is

21. Check Point 3.2 Expression Value y = 6x 6 + 3 * 5 12 / 2 – 4
3.10 Complete the table below by writing the value of each expression in the "Value" column.
Expression Value
6 + 3 * 5
12 / 2 – 4
* 2 – 6
% 3 – 1
(6 + 2 ) * 3
3.11 Write C++ expressions for the following algebraic expressions:
y = 6x
a = 2b + 4c
y = x2
x + 2
g = z2
y = 6 * x; 21 2
a = (2 * b ) + (4 * c ) ; 31 5
y = pow( x,2); 24
g = (x + 2) / pow( z,2);

22. 3.3 When you Mix Apples and Oranges: Type Coercion Rules
Rule 1 - Chars,shorts, and unsigned shorts are automatically promoted to int.
Rule 2 - If two values are of different types the lower-ranking one is promoted to the type of the higher-ranking on
Rule 3 - when the value of an expression is assigned to a variable it will be converted to the data type of the variable
Concept - When an operator's operands are of different data types, C++ will automatically convert them to the same data type

23. 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

24. Overflow and Underflow
If an integer variable overflows or underflows the value wraps back around
no warning or error message is generated
If a floating point variable overflows or underflows the result depends on the compiler.
Concept - When a variable is assigned a value that is too large or too small in range for that variables data type, the variable underflows or overflows

25. Program 3-9 or 3-8 version 4
//This program demonstrates integer overflow and underflow
#include <iostream>
using namespace std;
void main()‏ {
short TestVar = 32767;
cout << TestVar << endl;
TestVar = TestVar + 1;
TestVar = TestVar - 1; }
This program assumes that an integer is stored in two bytes of memory
Program Output
32767
-32768

26. Program 3-10 or 3-9 version 4 Program Output
//This program can be used to see
// how your system handles floating
// point overflow and underflow.
#include <iostream>
using namespace std;
void main()‏ {
float Test;
Test = 2.0e38 * 1000;
// Should overflow Test
cout << Test << endl;
Test = 2.0e-38 / 2.0e38;
// Should underflow Test }
This compiler does not generate a runtime error but the value stored may not be usable
Program Output
1.+INF

27. 3.5 The Typecast Operator
The typecast operator manually promotes or demotes a value
works on either an expression or a variable
the conversion is temporary
truncation may occur
Example:
Val = int(number);
Val = float(digit1) / digit2; //prevents integer divide
Val = float (digit1/digit2); //allows integer divide
Val = (int) number; // is also correct

28. Program 3-11 or 3-10 version 4 #include <iostream>
using namespace std;
void main()‏ {
int Months, Books;
float PerMonth;
cout << "How many books do you ";
cout << "plan to read? ";
cin >> Books;
cout << "How many months will ";
cout << "it take you to read them? ";
cin >> Months;
PerMonth = float(Books) / Months;
cout << "That is " << PerMonth
cout << " books per month.\n";
This program uses the type cast operator to avoid integer division
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.

29. 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 then the result is type cast to a float.
Type casting has no effect on the values it operates on. A temporary variable is created for the duration of the instruction.

30. Program 3-12 or 3-11 version 4 Program Output 65 A
/* This program uses a typecast operator to print a character from a number.*/
#include <iostream>
using namespace std;
void main()‏ {
int Number = 65;
cout << Number << endl;
cout << char(Number) << endl; }
Program Output 65 A

31. The Power of Constants Makes the program more readable
Simplifies maintenance
Example:
const float PI = ; or
#define PI
Using a named constant will not make the program run more efficiently
Concept - Constants may be given names that symbolically represent them in a program

32. Program 3-13 or 3-12 version 4 #include <iostream>
#include <math.h>
using namespace std;
void main()‏ {
const float Pi = ;
double Area, Radius;
cout << "This program calculates"; cout << " the area of a circle.\n";
cout << "What is the radius of ";
cout << " the circle? ";
cin >> Radius;
Area = Pi * pow(Radius,2);
cout << "The area is " << Area; }
The literal has been replaced with a floating point constant.
Program Output
This program calculates
the area of a circle.
What is the radius of
the circle?
5 [Enter]
The area is

33. 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= ;

34. Program 3-14 or 3-13 version 4 #include <iostream>
#include <math>
// needed for pow function
#define PI
using namespace std;
void main()‏ {
double Area, Radius;
cout << "This program calculates";
cout << " the area of a circle.\n";
cout << "What is the radius of the";
cout << " circle? ";
cin >> Radius;
Area = PI * pow(Radius, 2);
cout << "The area is " << Area;
}  
Remember that the preprocessor performs a textual substitution. So each instance of Pi becomes a floating point literal.
Program Output
This program calculates
the area of a circle.
What is the radius of the
circle?
5 [Enter]
The area is

35. Multiple Assignments Groups like-variables in one statement
May be used within an expression
has the lowest precedence of all arithmetic operations
Should be placed within parentheses
May be confusing if not clearly documented
Example:
a = b = c = d = 12 /
Concept - Multiple assignment means to assign the same value to several variables with one statement.

36. Combined Assignment Operators
Eliminates the need to enter the variable name twice
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;
Concept - The combined assignment operators make common arithmetic operations easier

37. 3.8 Formatting Output With String Manipulation
setw(n) n = the width of the display
setprecision(n) n = the number of significant digits or decimal places displayed
flags:
left
right
fixed
dec
hex
oct
scientific
showpoint
showpos
uppercase
Concept - The cout object provides ways to format data as it is being displayed.

38. Program 3-17 or 3-15 version 4 Program Output 2897 5 837 34 7 1623
//This program displays three rows of numbers
#include<iostream.h> 
using namespace std;
void main()‏ {
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; }
This program displays values with no output formatting. There is no column alignment.
Program Output

39. Program 3-18 or 3-16 version 4
The setw command is used to line up the columns. The default is right justified
/*This program displays three rows of numbers. */
#include <iostream>
#include <iomanip>
using namespace std;
void main()‏ {
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;
// 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; }
Program Output

40. Program 3-19 or 3-17 version 4 Program Output ( 3928)‏ ( 91.5)‏
/* This program demonstrates the setw manipulator being used with values of various data types. */
#include <iostream>
#include <iomanip>
using namespace std;
void main()‏ {
int IntValue = 3928;
float FloatValue = 91.5;
char StringValue[14] = "John J. Smith";
cout << "(" << setw(5);
cout << IntValue << ")" << endl;
cout << "(" << setw(8);
cout << FloatValue << ")" << endl;
cout << "(" << setw(16);
cout << StringValue << ")" << endl; }
setw can format the output of any data type
Program Output
( 3928)‏
( )‏
( John J. Smith)‏

41. 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.

42. Program 3-20 or 3-18 version 4 Program Output
/* This program demonstrates how setprecision rounds floating point value. */ 
#include <iostream>
#include <iomanip>
using namespace std;
void main()‏ {
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; }
setprecision does not truncate numbers it rounds them up
Program Output
4.9188
4.919
4.92
4.9 5

43. Table 3-11 Number Manipulator Value Displayed
setprecision(3) 28.9
21. setprecision(5) 21
109.5 setprecision(4) 109.5
setprecision(2) 34
cout << fixed;
setprecision(3)
21. setprecision(5)
109.5 setprecision(4)
setprecision(2) 34.29

44. Program for Table 3.11 #include <iostream>
#include <iomanip>
using namespace std;
void main()‏ {
cout << " Number\t\tManipulator\t\tValue Displayed\n";
cout <<" \t setprecision(3)\t"<< setprecision(3) << << endl;
cout <<"21.\t\t setprecision(5)\t"<< setprecision(5) << 21. << endl;
cout <<"109.5\t\t setprecision(4)\t"<< setprecision(4) << << endl;
cout <<" \t setprecision(2)\t"<< setprecision(2) << << endl;
cout <<" \t setprecision(1)\t"<< setprecision(1) << << endl;
cout << fixed;
cout << “fixed\n"; }

45. Program 3-21 or 3-19 version 4
This program will display 5 significant digits. But what if the total takes 6
/* This program asks for sales figures for 3 days. The total sales is calculated and displayed in a table*/
#include <iostream>
#include <iomanip>
using namespace std;
void main()‏ {
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;
cout << "\nSales Figures\n";
cout << " \n";
cout << setprecision(5);
cout << "Day 1: " << setw(8) << Day1;
cout << endl;
cout << "Day 2: " << setw(8) << Day2;
cout << "Day 3: " << setw(8) << Day3;
cout << "Total: " << setw(8) << Total; }

46. Program Output Enter the sales for day 1: 321.57 [Enter]
Sales Figures
Day 1:
Day 2:
Day 3:
Total: The value has been truncated

47. Program 3-22 or 3-20 version 4
#include <iostream>
#include <iomanip>
using namespace std;
void main()‏ {
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;
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; }
Program Output (modified)
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:
The decimal point is displayed only if there are digits to the right of it.

48. 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 or when it has all the character it needs.
White space characters include the [Enter] key, space, and tab.

49. Program 3-28 or 3-22 version 4 // This program demonstrates cin's
cin.getline will read one less character than the second parameter specifies to make room for the NULL character
// This program demonstrates cin's
// getline member function.
#include <iostream>
#include <iomanip>
using namespace std;
void main()‏ {
char String[81];
cout << "Enter a sentence: ";
cin.getline(String, 81);
cout << "You entered ";
cout << String << endl; }
Program Output
Enter a sentence:
To be, or not to be. [Enter]
You entered
To be, or not to be.

50. Program 3-29 or 3-23 version 4 #include <iostream>
#include <iomanip>
using namespace std;
void main()‏ {
char Ch;
cout << "Type a character
cout << " and press
cout << " Enter: ";
cin >> Ch;
cout << "You entered " << Ch << endl; }
cin requires that the user enter only a single. non white space character. All other input is ignored.
Program Output
Type a character
and press
Enter:
A [Enter]
You entered A

51. Program 3-30 or 3-23 version 4 #include <iostream>
#include <iomanip>
 using namespace std;
void main()‏ {
char Ch;
cout << "This program has"; cout << " paused. Press";
cout << " enter to continue.";
cin.get(Ch);
cout << "Thank you!";
cout << endl; }
cin.get will accept any key, particularly the return key
Program Output
This program has
paused. Press
Enter to continue.
[Enter]
Thank you!

52. Program 3-31 or 3-23? version 4 #include <iostream>
#include <iomanip>
using namespace std;
void main()‏ {
char Ch;
cout << "Type a character"; cout << " and press Enter: ";
cin.get(Ch);
cout << "You entered ";
cout << Ch << endl;
cout << "Its ASCII code is ";
cout << int(Ch) << endl; }
cin.get will accept non printable and white space characters
Program Output
Type a character and press Enter: [Enter]
You entered
Its ASCII code is 10

53. 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

54. More Mathematical Library Functions
abs
Absolute Value
exp ex
fmod
modulus for floating point
cos
cosine
sin
sine
tan
tangent
log
natural log
log10
base 10 log
sqrt
square root
Concept - The C++ runtime library provides several functions for performing complex mathematical operations.

55. Table 3-14 or 3-13 version 4 abs y = abs(x);
Returns the absolute value of the argument. The argument and the return value are integers.
cos y = cos(x);
Returns the cosine of the argument. The argument should be an angle expressed in radians. The return type and the argument are doubles.
exp y = exp(x);
Computes the exponential function of the argument, which is x. The return type and the argument are doubles.

56. Table 3-14 continued or 3-13 version 4
fmod y = fmod(x, z);
Returns, as a double, the remainder of the first argument divided by the second argument.
log y = log(x);
Returns the natural logarithm of the argument. The return type and the argument are doubles.
log10 y = log10(x);
Returns the base-10 logarithm of the argument. The return type and the argument are doubles.

57. Table 3-14 continued or 3-13 version 4
sin y = sin(x);
Returns the sine of the argument. The argument should be an angle expressed in radians. The return type and the argument are doubles.
sqrt y = sqrt(x);
Returns the square root of the argument. The return type and argument are doubles.
tan y = tan(x);
Returns the tangent of the argument. The argument should be an angle expressed in radians. The return type and the argument are doubles.

58. Program 3-32 or 3-24 version 4
This program uses the sqrt function to find the hypotenuse of a right triangle
#include <iostream>
#include <math> // For sqrt
using namespace std;
void main()‏ {
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 ";
cout << "hypotenuse is "<< C << endl; }
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

59. Random Numbers y = rand(); (from the stdlib.h library)‏
returns pseudo-random number
C++ returns the same sequence of numbers each time the program executes
srand(x); (from the stdlib.h library)‏
seeds the random number generator so that a new sequence of numbers will be generated
Concept - Some programming techniques require the use of randomly generated numbers

60. Program 3-33 or 3-25 version 4
It still gives the same numbers for the same seed value
// This program demonstrates random
//numbers.
 #include <iostream>
#include <stdlib>
using namespace std;
void main()‏ {
unsigned Seed;
cout << "Enter a seed value: ";
cin >> Seed;
srand(Seed);
cout << rand() << endl; }
Program Output
Enter a seed value: 5
1731
32036
21622
Program Output with Other Example Input
Enter a seed value: 16
5540
29663
9920

61. Basic File I/O
The file fstream contains all the declarations necessary for file operations
#include <fstream>
It declares the following data types
ofstream used to open a file for output
ifstream used to open a file for input
fstream used to open a file for both input and output
You must declare an object of one of these data types
i.e ifstream InputFile;

62. Reading from a file
Once the file has been opened you can read data from it similar to the way cin is used
InputFile >> Variable_Name
The data is read in the order found in the file
You can create a file using notepad or any other word processor.
Make sure the file name matches the file name in the open statement exactly
The file must be in the same directory that the executable file is located or you will need to specify the exact path.