1 Conditional statements Dept. of Computer Engineering Faculty of Engineering, Kasetsart University Bangkok, Thailand

2 Conditional statement  In the previous lessons, all the statements in the programs are executed sequentially without skipping  Conditional statement Now, some statements may be executed only if certain conditions are satisfied, otherwise, the statements will be skipped number = int.Parse(Console.ReadLine()); if(number>=0) Console.WriteLine("The number is positive"); else Console.WriteLine("The number is negative");

3 Data type: bool  Boolean (bool when declared) is a logical data type. A value of a variable whose data type is boolean can be either true or false. Notes : A variable with type bool can not be read by input statement. However it can be displayed by output statement

4 static void Main(string[] args) { bool found; string fact; int year; Console.Write("Please enter faculty's name : "); fact = Console.ReadLine(); fact = fact.ToLower(); Console.Write("please enter year studying : "); year = int.Parse(Console.ReadLine()); if (((fact == "engineer")&& (year >= 2)) || ((fact == "sciences") && (year >=3))) found = true; else found = false; Console.WriteLine(found); }

5 class ClassBoolean { static void Main(string[] args) { Console.WriteLine(2+3 == 5); Console.WriteLine('A' < 'B'); Console.WriteLine("Engineer" == "engineer"); Console.WriteLine(3*4 == 7*4/2); } Output : true true false

6 Relational Operators  They are used to compare data items of the compatible type Relational Operator in Pascal Meaning ==Equal to >Greater than <Less than >=Greater than or equal to <=Less than or equal to !=Not equal to

7 Boolean Expression - Boolean Constants and Boolean Variable  Boolean constants and Boolean variables are of type bool static void Main(string[] args) { const bool sunRiseFromEast = true; const bool oneGreaterThanTwo = false; bool boy; Console.WriteLine("The sun rises from the east is " + sunRiseFromEast); boy = false; Console.WriteLine("It is " + boy + " that Paul is a boy"); }

8 Boolean Expression - Boolean Expressions with Operands of Arithmetic Expressions Boolean Expression Value 2.5 == 5false 4%10 > 1-3true 5.7 >= -2true 5/2 <= 1.1*2false 999!=999.9true

9 Boolean Expression - Boolean Expressions with Character Operands ASCII – American Standard Code for Information Interchange Contains 128 characters

10 Boolean Expression - Boolean Expressions with Character Operands  Characters are compared using their code values according to certain code system. Boolean Expression ’\’ != ’j’ ’9’ > ’4’ ’A’ >= ’a’ ASCII of First Operand ASCII of Second Operand Boolean Expression true false

11 Compound Boolean Expressions  Simple Boolean Expressions may be joined by logical operators to form compound Boolean expressions  Logical Operators && (and) || (or) ! (not)  Examples (age >= 18) && (age <=20) (grade == 'F') || (grade =='W')

12 Compound Boolean Expressions - Logical Operators  Truth Table for ‘and’ operator  Truth Table for ‘or’ operator Boolean expression PBoolean expression QP && Q TRUE FALSE TRUEFALSE Boolean expression PBoolean expression QP || Q TRUE FALSETRUE FALSETRUETURE FALSE

13 Compound Boolean Expressions - Logical Operators  Truth table for ‘not’ operator Boolean Expression P! Q TRUEFALSE TRUE

14 Precedence  The order of precedence is ‘!’, ‘&&’, ‘||’  The relational operators have lower precedence than logical operators OperatorPrecedence Level ( ) 1 ++, --, !, cast 2 *, /, % 3 +, - 4, >= 5 ==, != 6 && 7 || 8 int x = 3, y = 2, z = 4; Console.WriteLine(++x+3 >= y+6 && z>=4);

15 Boolean Expression Evaluation !('F' != 'M') || (19 > 12) && (19 < 18) !( true ) || (true) && (false) ( false ) || (true) && (false) ( false ) || ( false ) ( false )

16 Flowcharts  Graphical representation Terminator Process Input/output Condition Connector Flow line

17 Conditional Statements  Two kinds of conditional statements in C# are if statements and switch statements If statements If-else statements Nested if statements Switch statements