Socket ProgrammingLaboratory - 2

Logical/Conditional Operations

2

The if statement has the following syntax:

The if Statement

if ( condition ) statement;

if is a C#reserved word

The condition must be a boolean expression.It must evaluate to either true or false.

If the condition is true, the statement is executed.If it is false, the statement is skipped.

3

if Selection Structure (cont’d)

print “Passed”Grade >= 60true

false

if (studentGrade >= 60) Console.WriteLine (“Passed”);

// beginning of the next statement

4

if Selection Structure (cont’d)

print “Passed”Grade >= 60true

false

if (studentGrade >= 60){ Console.WriteLine (“Passed”);}

// beginning of the next statement

5

A condition often uses one of C#’s equality operators (==, !=) or relational operators (<, >, <=, >=), which all return boolean results:

== equal to!= not equal to< less than> greater than<= less than or equal to>= greater than or equal to

Boolean Expressions: Basics

Equality and Relational Operators

Standard algebraic equality operator or relational operator

C# equality or relational operator

Example of C# condition

Meaning of C# condition

Equality operators == x == y x is equal to y != x != y x is not equal to y Relational operators > > x > y x is greater than y < < x < y x is less than y >= x >= y x is greater than or equal to y <= x <= y x is less than or equal to y Equality and relational operators.

Question: if (grade = 100) Console.WriteLine( “Great!” );

using System;

class Comparison{ static void Main(string[] args) { int number1, number2;

// read in first number from user Console.Write("Please enter first integer: "); number1 = Int32.Parse(Console.ReadLine());

// read in second number from user Console.Write("\nPlease enter second integer: "); number2 = Int32.Parse(Console.ReadLine());

if (number1 == number2) Console.WriteLine(number1 + " == " + number2);

If Statement (Example)

if (number1 != number2) Console.WriteLine(number1 + " != " + number2);

if (number1 < number2) Console.WriteLine(number1 + " < " + number2);

if (number1 > number2) Console.WriteLine(number1 + " > " + number2); if (number1 <= number2) Console.WriteLine(number1 + " <= " + number2); if (number1 >= number2) Console.WriteLine(number1 + " >= " + number2); }}

If Statement (Example)

9

if/else Statement if ( <test> ) <code executed if <test> is true> ; else <code executed if <test> is false> ;

The if/else structure◦ Alternate courses can be taken when the

statement is false◦ Rather than one action there are two choices◦ Nested structures can test many cases

10

if/else Statement (cont’d) if ( <test> ) { <code executed if <test> is true> ; …… } else { <code executed if <test> is false> ; …… }

◦ Can use the block statement inside either branch

11

if/else Statement (cont’d)

Grade >= 60

print “Passed”print “Failed”

false true

if (studentGrade >= 60) Console.WriteLine (“Passed”);else Console.WriteLine (“Failed”);// beginning of the next statement

12

if/else Statement (cont’d)

Grade >= 60

print “Passed”print “Failed”

false true

if (studentGrade >= 60){ Console.WriteLine (“Passed”);}else Console.WriteLine (“Failed”);// beginning of the next statement

13

Nested if/else Statements

if (studentGrade >= 90) Console.WriteLine(“A”);else if (studentGrade >= 80) Console.WriteLine(“B”);else if (studentGrade >= 70) Console.WriteLine(“C”);else if (studentGrade >= 60) Console.WriteLine(“D”);else Console.WriteLine(“F”);

// beginning of the next statement

The statement executed as a result of an if statement or else clause could be another if statement

These are called nested if /else statements

14

Boolean expressions can also use the following logical and conditional operators:

! Logical NOT& Logical AND| Logical OR^ Logical exclusive OR

(XOR) && Conditional AND

|| Conditional OR

They all take boolean operands and produce boolean results

More Complex (Compound) Boolean Expressions: Logical Operators

Logical and Conditional Operatorsexpression1 expression2 expression1 &&

expression2 false false false false true false true false false true true true Truth table for the && (logical AND) operator.

expression1 expression2 expression1 || expression2

false false false false true true true false true true true true Truth table for the || (logical OR) operator.

Logical and Conditional Operators

expression1 expression2 expression1 ^ expression2

false false false false true true true false true true true false Truth table for the logical exclusive OR (^) operator.

expression !expression false true True false Truth table for operator! (logical NOT).

Program & Test

18

The switch Statement The switch statement provides another

means to decide which statement to execute next

The switch statement evaluates an expression, then attempts to match the result to one of several possible cases

Each case contains a value and a list of statements

The flow of control transfers to statement list associated with the first value that matches

19

The switch Statement: Syntax

The general syntax of a switch statement is:

switch ( expression ){ case value1 : statement-list1 case value2 : statement-list2 case ...

default : statement-list}

If expressionmatches value2,control jumpsto here

switchandcaseanddefaultarereservedwords

20

The switch Statement

break;

case: a case a action(s)true

false

.

.

.

break;

case b action(s) break;

false

falsecase: z case z action(s) break;

default action(s)

true

true

case: b

using System;

class SwitchSelect{ public static void Main() { string myInput; int myInt;

Console.Write("Please enter a number between 1 and 3: "); myInput = Console.ReadLine(); myInt = Int32.Parse(myInput);

// switch with integer type switch (myInt) { case 1: Console.WriteLine("Your number is {0}.", myInt); break; case 2: Console.WriteLine("Your number is {0}.", myInt); break; case 3: Console.WriteLine("Your number is {0}.", myInt); break; default: Console.WriteLine("Your number {0} is not between 1 and 3.", myInt); break; } }}

Example – 1 (Switch)

using System;

class SwitchSelect{ public static void Main() { string myInput; int myInt;

begin:

Console.Write("Please enter a number between 1 and 3: "); myInput = Console.ReadLine(); myInt = Int32.Parse(myInput);

// switch with integer type switch (myInt) { case 1: Console.WriteLine("Your number is {0}.", myInt); break; case 2: Console.WriteLine("Your number is {0}.", myInt); break; case 3: Console.WriteLine("Your number is {0}.", myInt); break; default: Console.WriteLine("Your number {0} is not between 1 and 3.", myInt); break; }

Example – 2 (Switch)

decide:

Console.Write("Type \"continue\" to go on or \"quit\" to stop: "); myInput = Console.ReadLine();

// switch with string type switch (myInput) { case "continue": goto begin; case "quit": Console.WriteLine("Bye."); break; default: Console.WriteLine("Your input {0} is incorrect.", myInput); goto decide; } }}

Example – 2 (Switch) Cont’d

using System;class SwitchTest{ static void Main() { Console.WriteLine("Coffee sizes: 1=Small 2=Medium 3=Large"); Console.Write("Please enter your selection: "); string s = Console.ReadLine(); int n = int.Parse(s); int cost = 0; switch (n) { case 1: cost += 25; break; case 2: cost += 25; goto case 1; case 3: cost += 50; goto case 1; default: Console.WriteLine("Invalid selection. Please select 1, 2, or 3."); break; } if (cost != 0) { Console.WriteLine("Please insert {0} cents.", cost); } Console.WriteLine("Thank you for your business."); }}

Example – 3 (Switch)

Option DescriptionStep Into If the current line contains a method, the

execution point will traverse deeper into the method definition.

Step Over If the current line contains a method, the execution point will not move further into the method definition

Step Out If the current line is within a method definition, the execution point will move out of the current method and back to the point before calling the method

Tracing and Debugging