C++ Programming, Namiq Sultan1 Chapter 3 Expressions and Interactivity Namiq Sultan University of Duhok Department of Electrical and Computer Engineerin

C++ Programming, Namiq Sultan 1

Chapter 3 Expressions and Interactivity

Namiq Sultan

University of Duhok

Department of Electrical and Computer Engineerin

Reference: Starting Out with C++, Tony Gaddis, 2nd Ed.


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.


Program 3-1

#include <iostream>

using namespace std;

int main()

{

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";

return 0;

}


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.


Entering Multiple Values

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

cin >> length>> width;


Reading Strings

• cin can read strings as well as numbers.

• Strings are stored in character arrays.

char Company[12];


Program 3-5

// This program demonstrates how cin can read a

// string into a character array

#include <iostream>


int main()

{

char name[21];

cout << "What is your name? ";

cin >> name;

cout << "Good morning " << name << endl;

return 0;

}


Program Output

What is your name? Charlie [Enter]

Good morning Charlie


Program 3-6

// This program reads two strings into two character arrays.

#include <iostream>


int main()

{

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;

return 0;

}


Program Output

Enter your first and last names and I will

reverse them.

Johnny Jones [Enter]

Jones, Johnny


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.


3.2 Mathematical Expressions

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


Program 3-7

// This program asks the user to enter the numerator// and denominator of a fraction and it displays the decimal value#include <iostream>using namespace std;int main(){

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);

return 0;}


Program Output for Program 3-8 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


Table 3-1 Precedence of Arithmetic Operators (Highest to Lowest)

(unary negation) -

* / %

+ -


Table 3-2 Some Expressions

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, either right to left or left to right


Table 3-3 Associativity of Arithmetic Operators Operator Associativity (unary negation) - Right to left

* / % Left to right

+ - Left to right


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


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


Program 3-8

// 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>

#include <math.h> // needed for the pow function


int main()

{

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;

return 0;

}


Program 3-8 Output With Example Input

This program calculates the area of a circle.What is the radius of the circle? 10[Enter]The area is 314.159


3.3 Type Conversion

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


Type Conversion 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.


3.5 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


Program 3-11#include <iostream>


int main()

{

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";

return 0;

}


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.


Program 3-12

// This program uses a typecast operator to print

// a character from a number.

#include <iostream>


int main()

{

int number = 65;

cout << number << endl;

cout << char(number) << endl;

return 0;

}


Program Output

65A


3.6 The Power of Constants

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


Program 3-13

// This program calculates the area of a circle.#include <iostream>#include <math.h>using namespace std;int main(){

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;return 0;

}


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;


Program 3-14

#include <iostream>

#include <math.h> // needed for pow function


#define PI 3.14159

int main()

{

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;

return 0;

}


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;


Combined Assignment

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;


3.10 More Mathematical Library Functions


Table 3-14

ab s Example Usage: y = abs(x);

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

cos Example Usage: y = cos(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.

exp Example Usage: y = exp(x);

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


Table 3-14 continuedfmod Example Usage: y = fmod(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.

log Example Usage: y = log(x);

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

log10 Example Usage: y = log10(x);

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


Table 3-14 continued

sin Example Usage: y = sin(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.

sqrt Example Usage: y = sqrt(x); Description Returns the square root of the argument. The return type and

argument are doubles.

tan Example Usage: y = tan(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.

41

Program 3-32// 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>

#include <math.h> // For sqrt and pow


int 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 << "The length of the hypotenuse is ";

cout << c << endl;

return 0;

}


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

Documents

C++ Programming, Namiq Sultan1 Chapter 3 Expressions and Interactivity Namiq Sultan University of Duhok Department of Electrical and Computer Engineerin