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					Module3
Selection Statement

Dr. Pattara Leelaprute
ดร. ภทร ลลาพฤทธ
Computer Engineering Department
Kasetsart University
pattara.l@ku.ac.th
http://www.cpe.ku.ac.th/~pattara
                                   1
Outline
   n Boolean expression
   n if statement
   n nested if statement
   n switch case statement




                             2
Boolean Expression
  n   Operators
      ¨ Comparison
        n Equal ==
        n Not equal !=

        n Less <

        n Greater >

        n Less than or equal to <=

        n Greater than or equal to >=

      ¨ Boolean
        n And &&
        n Or ||

        n Not !                         3
Boolean Expression Example
 n   From the equation: X2+9X+10 = 0
     ¨ How can we check that value of X is the
       answer for above equation?
        ((X*X +9*X +10) == 0) //true if X is the answer


 n   Condition: Is value Y even number?
                (Y%2 == 0) //true if Y is even
                              OR
                 (Y%2 != 1) //true if Y is even
                                                          4
Example: Boolean Expressions
 double x = 4.0;

 Expression   Value
 x < 5.0        true
              ___________
 x > 5.0        false
              ___________
 x <= 5.0     ___________
                true
 5.0 == x       false
              ___________
 x != 5.0       true
              ___________

                            5
Outline
   n Boolean expression
   n if statement
   n nested if statement
   n switch case statement




                             6
if statement
   n Execute the specific statement when
     the ”condition” becomes true
   n Syntax:

 if (condition)         if (condition) {
  statement; //true         statement1; //true
                            statement2; //true
                        }


                                             7
if statement example
n   BMI (Body Mass Index)
                      Weight in Kilograms
       BMI =
              (Height in Meters) X (Height in Meters)

               BMI                  Weight Status
            Below 18.5     Underweight
           18.5 – 24.9     Normal
           25.0 – 29.9     Overweight
          30.0 and Above   Obese (Extremely Fat)


                                                    8
if…else… statement
   n  If condition is true à execute
      statement1
    n If condition is false à execute
      statement2           if (condition)
if (condition)
    n Syntax:                statement1; //true
 statement1; //true
                           else {
else
                               statement2; // false
 statement2; // false
                               statement3; // false
                           }
                                                  9
if…else… statement example
  n   Question
      ¨ Value   in variable N is Odd or Even Number?

   Value in N                   Output
  Even Number               It’s even number.
  Odd Number                 It’s odd number.

      if (___________________)
        Console.WriteLine(“It’s even number.”);
      else
        Console.WriteLine(“It’s odd number.”);
                                                       10
Exercise 1: Separated IF (simple)
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”);}
                                                  11
Exercise 2: Related two IF (full version)
  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”);}
  }                                                      12
Exercise 2: Related two IF (short version)
  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 if (like_friedrice==true)
      {Console.WriteLine(“I like friedrice”);}
 else
     {Console.WriteLine(“I don’t like friedrice”);}



                                                         13
Quiz
n   Fill the following blank
          if (___________________)
                   X%2 == 0
            Console.WriteLine(“It’s even number.”);
          else
            Console.WriteLine(“It’s odd number.”);

n   What x, y, z are called ?
                x1
                x2            y               z

n   Rewrite this sentence
         int Width,High;
         Width=10;                          int   _______;
         High=5;                            int   _______;

n   10110102 = ?          Hint: 26 + 24 + 23 + 21 = ?        14
Outline
   n Boolean expression
   n if statement
   n nested if statement
   n switch case statement




                             15
Nested if statement
  int N;
  N = int.Parse(Console.ReadLine());
                                             if#1
  if (N >= 0)
  {                                         if#2
    if (N==0)
       Console.WriteLine(“N is zero number”);
    else
       Console.WriteLine(“N is positive number”);
  }
  else
     Console.WriteLine(“N is negative number”);




                                                    16
Nested IF Overview
             if#1         if#1
           if#2
         if#3
                        else#1
                    =
                         if#2
                        if#3




                                 17
Nested if statement
                  2x+10,    x≤ 5

       f(x) =     x2+10,    5 < x ≤ 20

                  x3+10,    x > 20

       Range          Boolean Expression
        x≤ 5                  (x <= 5)
     5 < x ≤ 20        ((5 < x) && (x <= 20))
       x > 20                 (x > 20)
                                                18
Nested if statement
  double fx = 0;
  double x = double.Parse(Console.ReadLine());

  #1 if (         X <= 5         )
  #2      fx = 2*x + 10;
  #3 else if (       5 < x <= 20   )
  #4          fx = x*x + 10;
  #5     else
  #6         fx = x*x*x + 10;
  #7
  #8 Console.WriteLine(“f(x) = {0}”, fx);

                2x+10,     x≤ 5
      f(x) =    x2+10,     5 < x ≤ 20
                x3+10,     x > 20
                                                 19
Exercise 3: Nested two IF (short version)
  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”);}
    }
 else if (like_friedrice==true)
       {Console.WriteLine(“I like fried rice”);}
 else
      {Console.WriteLine(“I don’t like fried rice”);}     20
Outline
   n Boolean expression
   n if statement
   n nested if statement
   n switch case statement




                             21
switch…case statement
  n   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   22
Example: switch-case (1)
                        int day_num;
    int     day name    Console.Write("Input the day");
 day_num;
                        day_num =
    1        Sunday           int.Parse(Console.ReadLine());

    2        Monday     switch(day_num)
                                 day_num      <expression>
                        {case 1:
    3        Tuesday       Console.Write ("Today is Sunday");
                           break;
    4       Wednesday               <constant-expression>
                          case 2:
    5       Thursday       Console.Write("Today is Monday");
                           break;
    6         Friday         :
    7        Saturday     default :
                           Console.Write ("I don’t know");
                           break;
                        }                                  23
  Example: switch-case (2)
                        int month;
int month;    month     Console.Write("Input Month");
                        month = int.Parse(Console.ReadLine());
    1        January
                        switch(month)
                                 month
    2        February   {case 1:
                          case 3:
    3         March       case 5:
                          Console.Write("This month has 31days");
    4          April       break;
                          case 4:
   …           …..        case 6:
                          Console.Write("This month has 30days");
                           break;
   …           …..        default :
                           Console.Write ("Input again");
   12        December      break;
                        }

                                                                 24
   Example: switch-case (3)
      <expression> must be int, char, string
         char version                        int version
char op;                           int day_num;
Console.Write("Select + - / * :"); day_num=
op=char.Parse(Console.ReadLine()); int.Parse(Console.ReadLine());

switch(op)                          switch(day_num )
{                                   {
                     <expression>
  case '+':                           case 1:
   Console.Write("{0}+{1}={2}",       Console.Write ("Sunday");
                        x,y,x+y);     break;
   break;        <constant-expression>
  case '-':                           case 2:
   Console.Write("{0}-{1}={2}",       console.Write("Monday");
                        x,y,x-y);     break;
   break;                                    :
    :                                 default :
  default:                             Console.Write(“Try again");
   Console.Write("Try again");         break;
   break;                           }
}                                                              25
Example: switch-case (4)
 <expression> must be int, char, string
        string op;
                         string version
        Console.Write("Select + - / * :");
        op=Console.ReadLine();

        switch(op)
        {                    <expression>
          case “+”:
           Console.Write("{0}+{1}={2}",
                                x,y,x+y);
           break;         <constant-expression>
          case “-”:
           Console.Write("{0}-{1}={2}",
                                x,y,x-y);
           break;
            :
          default:
           Console.Write("Try again");
           break;
        }                                         26
 Convert switch-case to if else
       switch version with default            if else version
int a;
a=                                    if (a == 1 || a == 2)
int.Parse(Console.ReadLine());         Console.WriteLine("Hi");

switch (a) {     <expression>         else if (a == 3 || a == 4)
  case 1 :       must be               Console.WriteLine("Hello");
  case 2 :       int , char, string
                                      else
   Console.WriteLine("Hi");            Console.WriteLine("Bye");
   break;
                 <constant-
  case 3 :
                 expression>           switch version without default
  case 4 :
   Console.WriteLine("Hello");
                                      switch (a) {
   break;
                                        case 1 :
  default :
                                        case 2 :
   Console.WriteLine("Bye");
                                         Console.WriteLine("Hi");
   break;
                                         break;
}
                                      }
                                                                 27
Flowchart Symbols Overview
   n   Graphical representation
                         Terminator

                         Process

                         Input/output

                         Condition

                         Connector
                          Flow line

                                        28
Program Flowchart Example
              START


            statement1


            statement2


            statement3


            statement4


              END


                            29
if statement flowchart
                  START

                             statement1
                statement1
                             if (condition)
                                 statement 2; // true
                CONDITION
                             else {
 false                true       statement 3; // false
 statement3     statement2   }
                             statement 4;


         statement4

                                                         30
Quiz2
  n   Fill           blanks in the program.
  n   Write the program flowchart.
                  2x+10,   x≤ 5
         f(x) =  x2+10,    5 < x ≤ 20
                 x3+10,    x>
  double fx = 0; 20
  double x = double.Parse(Console.ReadLine());

  if (                      )
      fx = 2*x + 10;
  else if (                     )
          fx = x*x + 10;
       else
          fx = x*x*x + 10;
  Console.WriteLine(“f(x) = {0}”, fx);
                                                 31
Summary
  n Boolean Expression
  n Selection Statements
                 Statement
      ¨ if...else...
      ¨ switch-case Statement
                       Selection Problems


                         switch
                       if…else…




                                            32

				
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posted:7/2/2013
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