Selection Statement – Selection Statement Modified from Aj. Thanachat Thanomkulabut’s slide 1 st semester, 2012

Outline 2  Boolean expression  Flowchart  if  if statement  if…else…  if…else… statement  nested if  nested if statement  switch case  switch case statement

Boolean expression  Operators  Comparison == Equal == != Not equal != < Less < > Greater > <= Less than or equal to <= >= Greater than or equal to >=  Boolean && And && || Or || ! Not ! 3 Boolean Expression 0 and 0 = 0 0 and 1 = 0 1 and 0 = 0 1 and 1 = 1 0 or 0 = 0 0 or 1 = 1 1 or 0 = 1 1 or 1 = 1 not 0 = 1 not 1 = 0

Boolean expression 4 int Y; Y Is Y greater than 3? Y>3 Is Y less than 5? Y<5 Is Y between 3 and 5? (Y<5)(Y>3)&& Boolean Expression

Boolean Expression Example  From the equation: X 2 +9X+10 = 0  How can we check that value of X is the answer for above equation?  Condition: Is Y an even number? //true if X is the answer ((X*X +9*X +10) == 0) //true if X is the answer //true if Y is even (Y%2 == 0) //true if Y is evenOR //true if Y is even (Y%2 != 1) //true if Y is even 5 Boolean Expression

Example: Boolean Expressions double x = 4.0; Expression Value x < 5.0 ___________ x > 5.0 ___________ x <= 5.0 ___________ 5.0 == x ___________ x != 5.0 ___________ (3!=4)&&(7<5) ___________ (4>4)||(5<=10) ___________ true false true false true 6 Boolean Expression false true

Boolean variable  Used for storing Boolean value  true  false  Keyword: bool  Usage example: int X = 0; bool MyVar = true; //Boolean variable declaration MyVar = (X>0); //Boolean expression 7 Boolean variable

Outline 8  Boolean expression  Flowchart  if  if statement  if…else…  if…else… statement

Flowchart symbols overview  Graphical representation Terminator Process Input/output Condition Connector Flow line 9 Flowchart

Program flowchart example Start Statement1 Statement2 Statement3 Statement4 End 10 Flowchart

Outline 11  Boolean expression  Flowchart  if  if statement  if…else…  if…else… statement

if statement ”condition”true  Execute the specific statement when the ”condition” becomes true  Syntax: if (condition) statement; statement; if (condition) { statement1; statement1; statement2; statement2;} if (condition) { statement; statement;} 12 if statementtrue true

13 condition False True Statement if (condition) statement; statement; if (condition) { statement; statement;} if statement

14 condition False True Statement1 Statement2 if (condition) { statement1; statement1; statement2; statement2;} if statement

if statement with Boolean variable 15 bool Y; int X = int.Parse(Console.ReadLine()); Y = (X > 10); if (Y) console.Write(“X is greater than 10”); else console.Write(“X is less than or equal to 10”); if statement

16 if statement example  BMI (Body Mass Index) BMIWeight Status Below 18.5Underweight 18.5 – 24.9Normal 25.0 – 29.9Overweight 30.0 and AboveObese (Extremely Fat) BMI = Weight in Kilograms (Height in Meters) X (Height in Meters) 16

if statement BMIWeight Status Below 18.5Underweight 18.5 – 24.9Normal 25.0 – 29.9Overweight 30.0 and AboveObese (Extremely Fat) BMI = Weight in Kilograms (Height in Meters) X (Height in Meters) 17 double BMI = W /(H*H); if(BMI<18.5) Console.WriteLine(“Underweight”); Console.WriteLine(“Underweight”); if(BMI>=18.5 && BMI =18.5 && BMI<=24.9) Console.WriteLine(“Normal”); Console.WriteLine(“Normal”); if(BMI>=25.0 && BMI =25.0 && BMI<=29.9) Console.WriteLine(“Overweight”); Console.WriteLine(“Overweight”); if statement example if(BMI>=30.0) Console.WriteLine(“Obese”); Console.WriteLine(“Obese”);

if statement Test I  Selfish Ratio RatioOutput More than 1You are selfish 1You break even Less than 1You are giver 18 Selfish Ratio =RecievingGiving

Outline 19  Boolean expression  Flowchart  if  if statement  if…else…  if…else… statement

if…else… statement flowchart statement1; if (condition) { statement2; //true statement2; //true} else { statement3; //false statement3; //false}statement4; Start Statement1 Condition Statement2 Statement3 true false Statement4 End 20 Flowchart

if…else… statement conditiontruestatement1  If condition is true  execute statement1 conditionfalsestatement2  If condition is false  execute statement2  Syntax: if (condition) statement1; //true statement1; //trueelse statement2; //false if (condition) statement1; //true statement1; //true else { statement2; //false statement2; //false statement3; //false } 21 if…else… statement

22 condition False True Statement2 Statement1 if (condition) statement1; //true statement1; //trueelse statement2; //false if…else… statement

23 if (condition) statement1; //true statement1; //true else { statement2; //false statement2; //false statement3; //false } condition False True Statement2 Statement1 Statement3 if…else… statement

if… else… statement flowchart 24 n= int.Parse(Console.ReadLine()); if (n>0) n= 2*n+5; n= 2*n+5; else { Console.Write(“Go”); Console.Write(“Go”); n = n%4; n = n%4;} Start n>0 n=2*n+5; true false n=n%4; End n=int.Parse(Console.ReadLine()); Console. Write(“Go”); Flowchart

if…else… statement example 25  Write a program that checks if the input number is odd or even.  input : integer number  output : message to inform that number is odd or even. Value in NOutput Even NumberIt’s even number. Odd NumberIt’s odd number. if…else… statement

if…else… statement example 26 Value of nOutput Even NumberIt’s even number. Odd NumberIt’s odd number. if(n%2 == 0) Console.WriteLine(“It’s even number”); Console.WriteLine(“It’s even number”); else Console.WriteLine(“It’s odd number”); Console.WriteLine(“It’s odd number”); if…else… statement

Test I 27  Write a program that computes the value of a f(x) based on the value of x  input : number x  output : f(x) f(x)x x 2 +1x<0 x+2x≥0 if…else… statement

Summary 28  Boolean expression  Flowchart  if  if statement  if…else…  if…else… statement  nested if  nested if statement  switch case  switch case statement

Any question?