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1
CS102Introduction 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
3
The cin Object• 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
Concept - The cin object reads information typed at the keyboard
4
Program 3-1#include <iostream.h>void main(void){
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"; cout <<" rectangle? ";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 therectangle? 10 [Enter]
What is the width of therectangle? 20 [Enter]
The area of the rectangle is 200.
This program will calculate the area of any rectangle
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;
}
Program Output
10 [Enter] 20 [Enter]
The area of the rectangle is 200.
This program does not let the user know what is needed as input.
6
The cin Object• 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 onceConcept - The cin object can gather multiple values at once
7
Program 3-3#include <iostream.h>void main(void){
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;
}
Program Output This program calculatesthe area of a rectangle.Enter the length and widthof the rectangle separatedby a space.10 20 [Enter]The area of the rectangle is200
This program accepts multiple entries on one line
8
Program 3-4 or 3-3 version 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, ";
cout << "and a character: ";cin >> Whole >> Fractional >> Letter;cout << "Whole: " << Whole << endl;cout << "Fractional: " << Fractional << endl;cout << "Letter: " << Letter << endl;
}
Program Output Enter an integer, a float, and a character: 4 5.7 b [Enter]
Whole: 4 Fractional: 5.7 Letter: b
Values of different data types can be entered on the same line. They must be entered in the correct order
9
Program 3-5 or 3-4 version 4
Program Output
What is your name? Charlie [Enter]
Good morning Charlie
// This program demonstrates how cin can read a string into a character array. */
#include <iostream.h>void main(void){
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.
10
Program 3-6 or 3-5 version 4
// 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";
cout << " names and I will\n";cout << "reverse them.\n"; cin >> First >> Last;cout << Last << ", " << First;cout <<endl;
}
Program Output Enter your first and lastnames and I willreverse them.Johnny Jones [Enter]Jones, Johnny
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
11
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.
12
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;A. 3.14B. 3C. 0D. Nothing, an error message is displayed
Check point 3.1
<iostream>
char
char customer[53];
13
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
Concept - C++ allows you to construct complex mathematical expressions using multiple operators and
grouping symbols
14
Program 3-7 or 3-6 version 4/* This program asks the user top enter the numerator and denominator of a fraction and it displays the decimal value*/
void main(void){
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 thedecimal value of a fraction.Enter the numerator: 3 [Enter]
Enter the denominator: 16 [Enter]
The decimal value is0.1875
Mathematical expressions can be used in cout statements. Note the inputs are integers but they are converted to floats for storage
15
Precedence• If two operators share an operand the one
with the highest precedence works firsthighest - (Unary negation)
* / %
Lowest + -
• Example 6 * 7 - 3 = 39 (not 24)
• Example 3 + 12 / 3 = 7 (not 5 )
Mathematical expressions are evaluated left to rightMathematical expressions are evaluated left to right
16
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
Associativity is the order in which an operator works with its operands
17
Grouping With Parentheses• Parentheses are used to force some
operations to be performed before others– examples:
(5+2)*4 = 28
10 / (5-3) = 5
(4 + 17 ) % 2 -1 = 0
18
No Exponents Please• Include the following file in your program to deal
with exponents:#include <cmath> (or math.h, old way)
• 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
Concept - C++ does not have an operator to raise a number to a power. A library function must be used
19
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 3.14159 */#include <iostream.h>#include <math.h>void main(void){
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 = 3.14159 * pow(Radius,2);cout << "The area is " << Area;
}
Program Output
This program calculates the
area of a circle.
What is the radius of the
circle?
10 [Enter]
The area is 314.159
This program uses the pow function to find the area of a circle
20
3.11 Write C++ expressions for the following algebraic expressions:
y = 6x
a = 2b + 4c
y = x2
x + 2
g =---------
z2
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
9 + 14 * 2 – 6
5 + 19 % 3 – 1
(6 + 2 ) * 3
Check Point 3.2
21
2
31
5
24
y = 6 * x;
a = (2 * b ) + (4 * c ) ;
y = pow( x,2);
g = (x + 2) / pow( z,2);
21
3.3 When you Mix Apples and Oranges: Type Coercion Rules
Concept - When an operator's operands are of different data types, C++ will automatically convert them to the same data type
Concept - When an operator's operands are of different data types, C++ will automatically convert them to the same data type
• 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
22
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
23
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
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
24
Program 3-9 or 3-8 version 4
//This program demonstrates integer overflow and underflow#include <iostream.h>void main(void){
short TestVar = 32767;cout << TestVar << endl;TestVar = TestVar + 1;cout << TestVar << endl;TestVar = TestVar - 1;cout << TestVar << endl;
}
Program Output 32767
-32768
32767
This program assumes that an integer is stored in two bytes of memory
25
Program 3-10 or 3-9 version 4
//This program can be used to see// how your system handles floating// point overflow and underflow.#include <iostream.h>void main(void){
float Test;Test = 2.0e38 * 1000;
// Should overflow Testcout << Test << endl;Test = 2.0e-38 / 2.0e38;
// Should underflow Testcout << Test << endl;
}
Program Output1.#INF
0
This compiler does not generate a runtime error but the value stored may not be usable
26
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
27
Program 3-11 or 3-10 version 4#include <iostream.h>
void main(void)
{
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";
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.
This program uses the type cast operator to avoid integer division
28
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.
29
Program 3-12 or 3-11 version 4/* 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;
}
Program Output
65
A
30
The Power of Constants• Makes the program more readable
• Simplifies maintenance
Example:
const float PI = 3.14159;
or
#define PI 3.14159
• 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
Concept - Constants may be given names that symbolically represent them in a program
31
Program 3-13 or 3-12 version 4#include <iostream.h>#include <math.h>void main(void){
const float Pi = 3.14159;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;
}
Program OutputThis program calculates the area of a circle.What is the radius of the circle? 5 [Enter]
The area is 78.5397
The literal 3.14159 has been replaced with a floating point constant.
32
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;
33
Program 3-14 or 3-13 version 4#include <iostream.h>#include <math.h>// needed for pow function#define PI 3.14159
void main(void){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;
}
Program OutputThis program calculates the area of a circle.What is the radius of the circle? 5 [Enter]The area is 78.5397
Remember that the preprocessor performs a textual substitution. So each instance of Pi becomes a floating point literal.
34
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.
Concept - Multiple assignment means to assign the same value to several variables with one statement.
/
35
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 easierConcept - The combined assignment operators make common
arithmetic operations easier
36
3.8 Formatting Output WithString 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
Concept - The cout object provides ways to format data as it is being displayed.
Concept - The cout object provides ways to format data as it is being displayed.
• dec• hex• oct• scientific
• showpoint• showpos • uppercase
37
Program 3-17 or 3-15 version 4//This program displays three rows of numbers#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 numberscout << Num1 << " "; cout << Num2 << " "; cout << Num3 << endl;// Display the second row of numberscout << Num4 << " "; cout << Num5 << " "; cout << Num6 << endl;// Display the third row of numberscout << Num7 << " ";cout << Num8 << " "; cout << Num9 << endl;
}
Program Output
2897 5 837
34 7 1623
390 3456 12
This program displays values with no output formatting. There is no column alignment.
38
Program 3-18 or 3-16 version 4
/*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;
// Display the second row of numbers
cout << setw(4) << Num4 << " ";
cout a<< 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
2897 5 837
34 7 1623
390 3456 12
The setw command is used to line up the columns. The default is right justified
39
Program 3-19 or 3-17 version 4
/* 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); cout << IntValue << ")" << endl;cout << "(" << setw(8);cout << FloatValue << ")" << endl;cout << "(" << setw(16);cout << StringValue << ")" << endl;
}
Program Output( 3928)
( 91.5)
( John J. Smith)
setw can format the output of any data type
40
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.
41
Program 3-20 or 3-18 version 4
/* This program demonstrates how setprecision rounds floating point value. */
#include <iostream.h>#include <iomanip.h>void main(void){
float Quotient, Number1 = 132.364,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;
}
Program Output
4.918774.91884.9194.924.95
setprecision does not truncate numbers it rounds them up
42
Table 3-11Number Manipulator Value
Displayed
28.92786 setprecision(3) 28.9
21. setprecision(5) 21
109.5 setprecision(4) 109.5
34.28596 setprecision(2) 34
cout << fixed;28.92786 setprecision(3) 28.928
21. setprecision(5) 21.00000
109.5 setprecision(4) 109.5000
34.28596 setprecision(2) 34.29
43
Program 3-21 or 3-19 version 4/* 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; int 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 << endl;
cout << "Day 3: " << setw(8) << Day3;
cout << endl;
cout << "Total: " << setw(8) << Total;
cout << endl;
return 0;
}
This program will display 5 significant digits. But what if the total takes 6
44
Program Output
Enter the sales for day 1: 321.57 [Enter]Enter the sales for day 2: 269.62 [Enter]Enter the sales for day 3: 1307.77 [Enter] Sales Figures-------------Day 1: 321.57Day 2: 269.62Day 3: 1307.8Total: 1899 The value has been truncated
45
Program 3-22 or 3-20 version 4#include <iostream>#include <iomanip>using namespace std;int 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) << fixed << 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;return 0;}
Program Output (modified) Enter the sales for day 1: 321.00
[Enter]Enter the sales for day 2: 869.26
[Enter]Enter the sales for day 3: 403.77
[Enter]Sales Figures------------- Day 1: 321 Day 2: 869.26Day 3: 403.77Total: 1594.90
The decimal point is displayed only if there are digits to the right of it.
46
Stream Manipulatorfixed Displays floating-point numbers in fixed
point notation.setw(n) Establishes a print field of n spaces.showpoint Causes a decimal point and trailing zeros
to be displayed, even if there is no fractional part.
setprecision(n) Sets the precision of floating-point numbers
left Causes subsequent output to be left justified.
right Causes subsequent output to be right justified.
47
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.
48
Program 3-28 or 3-22 version 4
// 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 "; cout << String << endl;
}
Program Output
Enter a sentence:
To be, or not to be. [Enter]
You entered
To be, or not to be.
cin.getline will read one less character than the second parameter specifies to make room for the NULL character
49
Program 3-29 or 3-23 version 4
#include <iostream.h>#include <iomanip.h>
void main(void){
char Ch;cout << "Type a character
cout << " and press cout << " Enter: ";cin >> Ch;cout << "You entered " << Ch << endl;
}
Program Output Type a character and press Enter: A [Enter] You entered A
cin requires that the user enter only a single. non white space character. All other input is ignored.
50
Program 3-30 or 3-23 version 4#include <iostream.h>#include <iomanip.h> void main(void){
char Ch;
cout << "This program has"; cout << " paused. Press";cout << " enter to continue.";cin.get(Ch);cout << "Thank you!"; cout << endl;
}
Program OutputThis program has paused. Press Enter to continue. [Enter]Thank you!
cin.get will accept any key, particularly the return key
51
Program 3-31 or 3-23? version 4#include <iostream.h>#include <iomanip.h>
void main(void){
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;}
Program Output
Type a character and press Enter: [Enter]
You entered
Its ASCII code is
10
cin.get will accept non printable and white space characters
52
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
53
More Mathematical Library Functions
• absAbsolute Value
• expex
• fmod– modulus for
floating point
Concept - The C++ runtime library provides several functions for performing complex mathematical operations.
Concept - The C++ runtime library provides several functions for performing complex mathematical operations.
• lognatural log
• log10base 10 log
• sqrtsquare root
• coscosine
• sinsine
• tantangent
54
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.
55
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.
56
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.
57
Program 3-32 or 3-24 version 4
#include <iostream.h>#include <math.h> // For sqrtvoid 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 ";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
This program uses the sqrt function to find the hypotenuse of a right triangle
58
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
Concept - Some programming techniques require the use of randomly generated numbers
59
Program 3-33 or 3-25 version 4
// 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; cout << rand() << endl; 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
It still gives the same numbers for the same seed value
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Basic File I/O• The file fstream.h contains all the declarations
necessary for file operations#include <fstream.h>• 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;
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Reading from a file• Once the file has been opened you can read data
from it similar to the way cin is usedInputFile >> 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.