Operators and Programming Constructs pot

The following is the syntax of the if...else construct: Console.WriteLine"The Year you have entered is a } else { Using Conditional Constructs The if…else Construct... Output of

Operators are used to compute results and compare

the data values of a program A program often

involves

decision-making and iterative tasks To accomplish

these tasks, programmers use various operators in

the conditional and looping constructs

This chapter discusses the types of operators used in C# language In addition, the conditional constructs

and the looping constructs are also discussed

In this chapter, you will learn to:

 Use various operators:

 Use conditional constructs

 Use looping constructs

Objectives

Applications use operators to process the data entered by a user Operators like + and - are used to process variables and return a value An operator is a set of one or more characters that is used for computations or comparisons Operators can transform one or more data values, called operands, into a new data value

Consider the following expression:

These operators are the symbols that are used to perform arithmetic operations on

variables The following table describes the commonly used arithmetic operators

Operator Description Example

Operator Usage Description

= X = 5; Stores the value 5 in the variable X

Arithmetic Assignment Operators

Arithmetic Assignment Operators

These operators are used to increment or decrement the value of an operand by 1 The following table explains the usage of the increment and decrement operators

++ ++Operand;

(Preincrement operator)

Or, Operand++;

(Postincrement operator)

Used to increment the value of an operand by 1

Y = ++X;

If the initial value of X is

5, after the execution of the preceding statement, values of both X and Y will be 6

Y = X++;

If the initial value of X is

5, after the execution of the preceding statement, value of X will be 6 and the value of Y will be 5 Operand;

(Predecrement operator)

Or, Operand ;

(Postdecrement operator)

Used to decrement the value of an operand by 1

Y = X;

If the initial value of X is

5, after the execution of the preceding statement, values of X and Y will be

4

Y = X ;

If the initial value of X is

5, after the execution of the preceding statement, value of X will be 4 and the value of Y will be 5 Unary Operators

Unary Operators

These operators are used to compare two values and perform an action on the basis of the result of that comparison Whenever you use comparison operator, the expression results

a boolean value ‘true’ or ‘false’ The following table explains the usage of commonly used comparison operators

Operator Usage Description Example

(In the following examples, the value of X is assumed to be 20 and the value of Y is assumed to

Logical operators are used to evaluate expressions and return a Boolean value The following table explains the usage of logical operators

Operator Usage Description Example

&& expression1 &&

expression2

Returns true if both expression1 and expression2 are true

! ! expression Returns true if

the expression is false

bool Result int x;

x = 20;

Result = (!( x == 10)) Console.WriteLine(“x is not equal to 10”);

The message “x is not equal to 10” is displayed because the expression used in the if statement is true

Logical Operators

Operator Usage Description Example

|| expression1 ||

expression2

Returns true if either expression1 or expression2 or both of them are true

^ expression1 ^

expression2

Returns true if either expression1 or expression2 is true It returns false if both expression1 and expression2 are true or if both expression1 and expression2 are false

Logical Operators

The ability to take decisions is fundamental to human beings Decision-making can be incorporated into programs as well This will result in determining the sequence in which

a program will execute instructions You can control the flow of a program by using conditional constructs Conditional constructs allow the selective execution of statements, depending on the value of the expressions associated with them The comparison

operators are required for evaluating the conditions The various conditional constructs are:

„ Theif else construct

„ Theswitch case construct

The if else conditional construct is followed by a logical expression where data is compared and a decision is made on the basis of the result of the comparison The

following is the syntax of the if else construct:

Console.WriteLine("The Year you have entered is a

}

else

{

Using Conditional Constructs

The if…else Construct

Console.WriteLine("The Year you have entered is not

a Leap Year {0}", Year);

The output of the preceding code is shown in the following figure

Output of the Leap Year

The else part in the if else construct is optional and can be omitted, as shown in the following code:

int var = 5;

if (var>0)

Console.WriteLine(“var is a positive number.”);

The if else constructs can be nested inside each other When nested together, the construct is known as cascading if else constructs The following code is an example

of the cascading if else construct:

int Number1, Number2, Number3;

Number1 = 10;

Number2 = 20;

Number3 = 30;

if (Number1 > Number2)

Console.WriteLine(“Number3 is the greatest.”);

The preceding code displays the greatest of three numbers

The cascading if else construct can also be used with logical operators The

following code is an example of converting the cascading if else construct to an if else construct by using logical operators:

int Number1, Number2, Number3;

Number1 = 10;

Number2 = 20;

Number3 = 30;

if ((Number1 > Number2) && (Number1 > Number3))

Console.WriteLine(“Number1 is the greatest”);

In the preceding code, the && operator is used to find the logical AND of two conditions The statement Console.WriteLine(“Number1 is the greatest”) is executed only if both the conditions evaluate to true

In case of a logical OR operator (||), if the first condition evaluates to true, the second condition is not evaluated

Another conditional construct available in C# is the switch case construct It is used when there are multiple values for a variable The following code is the syntax of the switch case construct:

The following code is an example of the complexif elseconstruct:

Theswitch caseconstruct evaluates an expression only once at the top of the

structure, where as theif elseconstruct evaluates the expression for each if

statement

The if else structure can be substituted with a switch case structure only if each else if statement in the if else construct evaluates the same

expression

To develop the required program, perform the following steps:

1 Select StartÆAll ProgramsÆAccessoriesÆNotepad.

2 Write the following program code in Notepad:

3 Select FileÆSave to save the program file The Save As dialog box opens

4 Enter “Calculator.cs” in the File name text box

Note

The filename is saved with cs extension, signifying that it is a C# program

5 Click the Save button in the Save As dialog box

6 Select StartÆAll ProgramsÆMicrosoft Visual Studio 2005ÆVisual Studio

ToolsÆVisual Studio 2005 Command Prompt to open the Visual Studio 2005 Command Prompt window

7 In the Visual Studio 2005 Command Prompt window, move to the location where

the program file is saved

8 Compile the program file by using the following command:

csc Calculator.cs

9 Execute the compiled program as:

Calculator.exe

10 Verify the output of the executed program

The following screen verifies the output of the executed program

Output of the Executed Calculator Program

Loop structures are used to execute one or more lines of code repetitively The following loop constructs are supported by C#:

„ Thewhile loop

„ Thedo while loop

„ Thefor loop

The while loop construct is used to execute a block of statements for a definite number of times, depending on a condition The while statement always checks the condition before executing the statements within the loop When the execution reaches the last statement in the while loop, the control is passed back to the beginning of the loop If the condition still holds true, the statements within the loop are executed again The execution of the statements within the loop continues until the condition evaluates to false

The following code is the syntax of the while loop construct:

continues until the value of var becomes greater than or equal to 200

The while Loop

Using Loop Constructs

The output of the preceding code when executed is as follows

Output of the while Loop Program

You can use the break statement to exit the while loop structure The following code is

an example of the break statement:

The do while loop construct is similar to the while loop construct Both iterate until the specified loop condition becomes false However, in the do while loop, the body of the loop is executed at least once and the condition is evaluated for subsequent iterations

The do…while Loop

The following code is the syntax of the do while loop construct:

This difference between the do while and whileloop constructs is shown in the following figure

Difference in Execution of the do while and while Loops

The for loop structure is used to execute a block of statements for a specific number of times The following code is the syntax of the for loop construct:

for (initialization; termination; increment/decrement)

True

Execute body

of Loop

Evaluate Condition

You can create an infinite loop by omitting all the three expressions, as shown in the following code:

Body of the for Loop

Exit the for Loop

Increment/Decrement

The following is an example of the for loop structure that displays integers between 10and 20:

The output of the preceding code is as follows

Output of the for Loop Program

Problem Statement

Write a program that generates the Fibonacci series up to 200

Solution

To create the required program, perform the following steps:

1 Select StartÆAll ProgramsÆAccessoriesÆNotepad.

2 Write the following program code in Notepad:

3 Select FileÆSave to save the program file The Save As dialog box is displayed

4 Enter “Fibonacci.cs” in the File name text box

5 Click the Save button in the Save As dialog box

6 Select StartÆAll ProgramsÆMicrosoft Visual Studio 2005ÆVisual Studio

ToolsÆVisual Studio 2005 Command Prompt to open the Visual Studio 2005 Command Prompt window

7 In the Visual Studio 2005 Command Prompt window, move to the location where

the program file is saved

8 Compile the program file by using the following command:

csc Fibonacci.cs

9 Execute the compiled program as:

Fibonacci.exe

10 Verify the output of the executed program

Activity: Fibonacci Series Using Loop Constructs

The following screen verifies the output of the executed program

Output of the Fibonacci Series

At times, there is a need to exit a loop before the loop condition is re-evaluated after

iteration As with a while loop, you can use the break statement to exit for loop The continuestatement is used to skip all the subsequent instructions and take the control back to the loop

The following code accepts five numbers and prints the sum of all the positive numbers: using System;

class BreakContinue

{

static void Main(string[] args)

{

int incr, SumNum, number;

for (SumNum = number = incr = 0; incr < 5; incr += 1) {

Console.WriteLine("Enter a positive number");

number = Convert.ToInt32(Console.ReadLine());

if (number <= 0) // Non-positive numbers

continue; // Continue to inctr+=1 in the forloop SumNum = SumNum + number;

Console.ReadLine();

}

}

The output of the preceding code is as follows

Output of the break and continue Program

Note

1 Consider the following code:

static void Main(string[] args)

The Convert.ToChar() converts a value to the char datatype

What will be the output if the input of the preceding code is x?

3 Which of the following operators can be used to evaluate an expression to true only

if both the conditions are true?

a &&

b ||

c >=

d !=

4 State whether the following statement is true or false:

The continue statement if used in the while and do while loop causes the program control to pass to the top of the loop avoiding the other statements in the loop

5 State whether the following statement is true or false:

A termination expression is evaluated at each iteration of the for loop

In this chapter, you learned that:

„ Operators are used to compute and compare values and test multiple conditions

„ You use arithmetic operators to perform arithmetic operations on variables like addition, subtraction, multiplication, and division

„ You can use arithmetic assignment operators to perform arithmetic operations and assign the result to a variable

„ The unary operators, such as the increment and decrement operators, operate on one operand

„ Comparison operators are used to compare two values and perform an action on the basis of the result of the comparison

„ Logical operators are used to evaluate expressions and return a Boolean value

„ Conditional constructs are used to allow the selective execution of statements The conditional constructs in C# are: