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Selection Statement

Selection Statement. Thanachat Thanomkulabut. Outline. Boolean expression if statement nested if statement switch case statement Flowchart. Boolean Expression. Boolean Expression. Operators Comparison Equal == Not equal != Less < Greater > Less than or equal to <=

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Selection Statement

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  1. Selection Statement Thanachat Thanomkulabut

  2. Outline • Boolean expression • if statement • nested if statement • switch case statement • Flowchart

  3. Boolean Expression Boolean Expression • Operators • Comparison • Equal == • Not equal != • Less < • Greater > • Less than or equal to <= • Greater than or equal to >= • Boolean • And && • Or || • Not ! 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

  4. Boolean Expression Boolean Expression Example • From the equation: X2+9X+10 = 0 • How can we check that value of X is the answer for above equation? • Condition: Is value Y even number? ((X*X +9*X +10) == 0) //true if X is the answer (Y%2 == 0) //true if Y is even OR (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 false true

  6. Outline • Boolean expression • if statement • nested if statement • switch case statement • Flowchart

  7. if statement if statement • Execute the specific statement when the ”condition” becomes true • Syntax: true if (condition) statement; if (condition) { statement1; statement2; } true if (condition){ statement; }

  8. if statement condition False True Statement if statement if (condition) statement; if (condition){ statement; }

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

  10. if statement Weight in Kilograms BMI = (Height in Meters) X (Height in Meters) if statement example 10 • BMI (Body Mass Index)

  11. if statement Weight in Kilograms BMI = (Height in Meters) X (Height in Meters) if statement example 11 double BMI = W /(H*H); if(BMI<18.5) Console.WriteLine(“Underweight”); if(BMI>=18.5 && BMI<=24.9) Console.WriteLine(“Normal”); if(BMI>=25.0 && BMI<=29.9) Console.WriteLine(“Overweight”); if(BMI>=30.0) Console.WriteLine(“Obese”);

  12. if statement Recieving Selfish Ratio = Giving Test I 12 • Selfish Ratio

  13. if statement if…else… statement 13 • If condition is true execute statement1 • If condition isfalse execute statement2 • Syntax: if (condition) statement1; //true else statement2; //false if (condition) statement1; //true else{ statement2; //false statement3; //false }

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

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

  16. if statement if…else… statement example • Write the program which check input number. • input : integer number • output : message to inform that number is odd or even.

  17. if statement if…else… statement example if(n%2 == 0) Console.WriteLine(“It’s even number”); else Console.WriteLine(“It’s odd number”);

  18. if statement Test II • Write the program which find the value of function • input : number • output :

  19. Outline • Boolean expression • if statement • nested if statement • switch case statement • FlowChart

  20. Nested if statement Nested if statement 20 int N; N = int.Parse(Console.ReadLine()); if (N >= 0) { if (N==0) Console.WriteLine(“N is zero number”); else Console.WriteLine(“N is positive number”); } else Console.WriteLine(“N is negative number”); if#1 if#2

  21. Nested if statement Nested if statement 21 int N; N = int.Parse(Console.ReadLine()); if (N > 0) Console.WriteLine(“N is positive number”); else if (N==0) Console.WriteLine(“N is zero number”); else Console.WriteLine(“N is negative number”); if#1 if#2

  22. Nested if statement N -5 3 0 -5 3 0 N is negative number N is positive number N is zero number 22 int N; N = int.Parse(Console.ReadLine()); if (N >= 0) { if (N==0) Console.WriteLine(“N is zero number”); else Console.WriteLine(“N is positive number”); } else Console.WriteLine(“N is negative number”); -5 >= 0 3 >= 0 0 >= 0  False True  False True

  23. Nested if statement Nested if statement N 3 -4 0 0 3 N is positive number N is zero number N is negative number -4 23 int N; N = int.Parse(Console.ReadLine()); if (N > 0) Console.WriteLine(“N is positive number”); else if (N==0) Console.WriteLine(“N is zero number”); else Console.WriteLine(“N is negative number”); -4 > 0 0 > 0 3 > 0 False True False True

  24. Exercise 1: SeparatedIF(simple) 24 1. Have you eaten lunch? 2. Do you like noodle? if (eaten==true) {Console.WriteLine(“I’ve already eaten”);} else {Console.WriteLine(“I’ve not eat yet”);} if (like_noodle==true) {Console.WriteLine(“I like noodle”);} else {Console.WriteLine(“I don’t like noodle”);}

  25. Exercise 2: Relatedtwo IF(full version) 25 1. Do you like noodle? 2. If you don’t like noodle, do you like fried rice? if (like_noodle==true) {Console.WriteLine(“I like noodle”);} else { Console.WriteLine(“I don’t like noodle”); if (like_friedrice==true) {Console.WriteLine(“I like friedrice”);} else {Console.WriteLine(“I don’t like friedrice”);} }

  26. Exercise 2: Relatedtwo IF(short version) 26 if (like_noodle==true) {Console.WriteLine(“I like noodle”);} elseif (like_friedrice==true) {Console.WriteLine(“I like friedrice”);} else {Console.WriteLine(“I don’t like friedrice”);} 1. Do you like noodle? 2. If you don’t like noodle, do you like fried rice?

  27. Exercise 3: Nestedtwo IF(short version) 27 1. Do you like noodle? 1.1 If you like noodle, do you love Sen-Yai? 1.2 If you don’t like noodle, do you like fried rice? if (like_noodle==true) {Console.WriteLine(“I like noodle”); if (love_SenYai==true) {Console.WriteLine(“I love Sen-Yai”);} else {Console.WriteLine(“I don’t love Sen-Yai”);} } elseif (like_friedrice==true) {Console.WriteLine(“I like fried rice”);} else {Console.WriteLine(“I don’t like fried rice”);}

  28. Nested if statement Nested if statement example • Write the program which show student’s grade • input : score of student • output :

  29. Nested if statement 2x+10, x ≤ 5 f(x) = x2+10, 5 < x ≤ 20 x3+10, x > 20 Test III • Write the program which calculation value of following function • input : value of x • output : function value of x according with ...

  30. Outline • Boolean expression • if statement • nested if statement • switch case statement • Flowchart

  31. เปรียบเทียบ “Read” แต่ละแบบ • Console.Read() • ผู้ใช้ใส่สตริงใดๆเข้ามา รอจนกว่าผู้ใช้จะเคาะ Return แล้วค่อยทำคำสั่งต่อไป • ให้ค่า int กลับมา เป็น int ที่แทนรหัส ASCII ของ character ตัวหน้าสุด • Console.Read() ถูกเรียกอีกครั้ง จะให้ค่า ASCII ของ character ถัดไป เมื่อถึงตัวสุดท้าย รอผู้ใช้เคาะ Return อีกครั้งจึงจะทำคำสั่งต่อไป • Console.ReadLine() • ให้ค่าสตริงตามที่ผู้ใช้พิมพ์เข้ามา รอจนกว่าเคาะ Return แล้วทำคำสั่งต่อไป • Console.ReadKey() • ให้ค่า character ที่ผู้ใช้พิมพ์ และทำคำสั่งต่อไปทันที

  32. using System;    class Program    {public static void Main(string[] args)        {            Console.Write("Input any string: ");char ch = (char)(Console.Read());            Console.WriteLine(ch);            ch = (char)(Console.Read());            Console.WriteLine(ch);            ch = (char)(Console.Read());            Console.WriteLine(ch);            ch = (char)(Console.Read());            Console.WriteLine(ch);            ch = (char)(Console.Read());            Console.WriteLine(ch);            Console.WriteLine("Hello World!");            Console.ReadKey(true);        }    }

  33. switch...case statement switch…case statement 33 • For selecting a statement where its label corresponds to the value of the switch expression. switch (<expression>) { case <constant-expression> : <statements>; break; [default: <statements>; break;] } <expression> must be int, char, string

  34. switch...case statement Example: switch-case (1) 34 int day_num; Console.Write("Input the day"); day_num = int.Parse(Console.ReadLine()); switch(day_num) {case1: Console.Write ("Today is Sunday"); break; case2: Console.Write("Today is Monday"); break; : default : Console.Write ("I don’t know"); break; } 1 2 30 <expression> <constant-expression>

  35. switch...case statement Test III • Write the program which show numbers of day in each months • input : Abbreviation of months • output : numbers of day in each months

  36. switch...case statement Example: switch-case (2) 36 string month; Console.Write("Input Month"); month = Console.ReadLine(); switch(month) {case“Jan”: case“Mar”: case“May”: Console.Write("This month has 31days"); break; case“Apr”: case“Jun”: Console.Write("This month has 30days"); break; default : Console.Write (“Wrong Input"); break; }

  37. switch...case statement Example: switch-case (3) <expression> must be int, char, string 37 char version int version char op; Console.Write("Select + - / * :"); op=char.Parse(Console.ReadLine()); switch(op) { case '+': Console.Write("{0}+{1}={2}", x,y,x+y); break; case '-': Console.Write("{0}-{1}={2}", x,y,x-y); break; : default: Console.Write("Try again"); break; } int day_num; day_num= int.Parse(Console.ReadLine()); switch(day_num ) { case 1: Console.Write ("Sunday"); break; case 2: console.Write("Monday"); break; : default : Console.Write(“Try again"); break; } <expression> <constant-expression>

  38. switch...case statement Example: switch-case (4) <expression> must be int, char, string 38 string version string op; Console.Write("Select + - / * :"); op=Console.ReadLine(); switch(op) { case “+”: Console.Write("{0}+{1}={2}", x,y,x+y); break; case “-”: Console.Write("{0}-{1}={2}", x,y,x-y); break; : default: Console.Write("Try again"); break; } <expression> <constant-expression>

  39. switch...case statement if else version if (a == 1 || a == 2) Console.WriteLine("Hi"); else if (a == 3 || a == 4) Console.WriteLine("Hello"); else Console.WriteLine("Bye"); switch version without default switch (a) { case 1 : case 2 : Console.WriteLine("Hi"); break; } Convert switch-case to if else 39 switch version with default int a; a= int.Parse(Console.ReadLine()); switch (a) { case 1 : case 2 : Console.WriteLine("Hi"); break; case 3 : case 4 : Console.WriteLine("Hello"); break; default : Console.WriteLine("Bye"); break; }

  40. Outline • Boolean expression • if statement • nested if statement • switch case statement • Flowchart

  41. Flowchart Flowchart Symbols Overview 41 • Graphical representation Terminator Process Input/output Condition Connector Flow line

  42. Flowchart Program Flowchart Example 42 Start Statement1 Statement2 Statement3 Statement4 End

  43. Flowchart if statement flowchart Start 43 statement1; if (condition) statement2; //true else{ statement3; //false } statement4; Statement1 Condition true false Statement2 Statement3 Statement4 End

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

  45. Test IV • Write flow chart which accord to following program n= int.Parse(Console.ReadLine()); n = n%5; if (n==2) Console.WriteLine(“Remainder is 2”); else{ n = n*10; } Console.WriteLine(“Program End”);

  46. Any question?

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