1 nd Semester Module3 Selection Statement Thanawin Rakthanmanon Create by: Aphirak Jansang Computer Engineering Department Kasetsart University, Bangkok THAILAND

1 nd Semester Outline  Boolean expression  if  if statement  nested if  nested if statement  switch case  switch case statement

1 nd Semester Boolean Expression  Operators Comparison ==  Equal == !=  Not equal != <  Less < >  Greater > <=  Less than or equal to <= >=  Greater than or equal to >= Boolean &&  And && ||  Or || !  Not !

1 nd Semester 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 value Y 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

1 nd Semester Example: Boolean Expressions double x = 4.0; Expression Value x < 5.0 ___________ x > 5.0 ___________ x <= 5.0 ___________ 5.0 == x ___________ x != 5.0 ___________ true false true false true

1 nd Semester Outline  Boolean expression  if  if statement  nested if  nested if statement  switch case  switch case statement

1 nd Semester if statement ”condition”true  Execute the specific statement when the ”condition” becomes true  Syntax: if (condition) statement; //true statement; //true if (condition) { statement1; //true statement1; //true statement2; //true statement2; //true}

1 nd Semester if statement example  BMI (Body Mass Index) BMIWeight Status Below 18.5 Underweight 18.5 – 24.9 Normal 25.0 – 29.9 Overweight 30.0 and Above Obese (Extremely Fat) BMI = Weight in Kilograms (Height in Meters) X (Height in Meters)

1 nd Semester if…else… statement conditiontrue statement1  If condition is true  execute statement1 conditionfalse statement2  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 }

1 nd Semester if…else… statement example  Question Value in variable N is Odd or Even Number? Value in NOutput Even Number It’s even number. Odd Number It’s odd number. if (___________________) Console.WriteLine(“It’s even number.”); Console.WriteLine(“It’s even number.”);else Console.WriteLine(“It’s odd number.”);

1 nd Semester Quiz  Fill the following blank  What x, y, z are called ?  Rewrite this sentence  = ? if (___________________) Console.WriteLine(“It’s even number.”); Console.WriteLine(“It’s even number.”);else Console.WriteLine(“It’s odd number.”); x1x1x1x1 x2x2x2x2 z y int Width,High; Width=10;High=5; int _______; Hint: = ? X%2 == 0

1 nd Semester Outline  Boolean expression  if  if statement  nested if  nested if statement  switch case  switch case statement

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

1 nd Semester Nested IF Overviewif#1if#2 if#3 if#1if#2 if#3 else#1 =

1 nd Semester Nested if statement f(x) = 2x+10, x ≤ 5 x 2 +10, 5 < x ≤ 20 x 3 +10, x > 20 RangeBoolean Expression x ≤ 5 (x <= 5) (x <= 5) 5 < x ≤ 20 ((5 < x) && (x <= 20)) x > 20 (x > 20)

1 nd Semester Nested if statement f(x) = 2x+10, x ≤ 5 x 2 +10, 5 < x ≤ 20 x 3 +10, x > 20 double fx = 0; double x = double.Parse(Console.ReadLine()); #1 if ( ) #2 fx = 2*x + 10; #3 else if ( ) #4 fx = x*x + 10; #5 else #6 fx = x*x*x + 10; #7 #8 Console.WriteLine(“f(x) = {0}”, fx); X <= 5 5 < x <= 20

1 nd Semester Outline  Boolean expression  if  if statement  nested if  nested if statement  switch case  switch case statement

1 nd Semester switch…case statement  For selecting a statement where its label corresponds to the value of the switch expression. switch ( ) { case : ; ; break; [default: ; ; break; break;] } must be int, char, string must be int, char, string

1 nd Semester Example: switch-case (1) int day_num; day name 1Sunday 2Monday 3Tuesday 4Wednesday 5Thursday 6Friday 7Saturday int day_num; Console.Write("Input the day"); day_num = int.Parse(Console.ReadLine()); day_num switch(day_num) 1: {case 1: Console.Write ("Today is Sunday"); break; 2: case 2: Console.Write("Today is Monday"); break; : : default : Console.Write ("I don’t know"); break; } <expression> <constant-expression>

1 nd Semester Example: switch-case (2) int month; month 1January 2February 3March 4April …….. … 12December int month; Console.Write("Input Month"); month = int.Parse(Console.ReadLine()); month switch(month) 1: {case 1: 3: case 3: 5: case 5: Console.Write("This month has 31day"); break; 4: case 4: 6: case 6: Console.Write("This month has 30day"); break; : default : Console.Write ("Input again"); break; }

1 nd Semester Example: switch-case (3) 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; } must be int, char, string must be int, char, string 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> int version char version

1 nd Semester Example: switch-case (4) 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; } must be int, char, string must be int, char, string string version <expression>

1 nd Semester Convert switch-case to if else 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; } switch version with default <expression> must be int, char, string if (a == 1 || a == 2) Console.WriteLine("Hi"); else if (a == 3 || a == 4) Console.WriteLine("Hello"); else Console.WriteLine("Bye"); if else version switch (a) { case 1 : case 2 : Console.WriteLine("Hi"); break; } switch version without default

1 nd Semester Flowchart Symbols Overview  Graphical representation Terminator Process Input/output Condition Connector Flow line

1 nd Semester Program Flowchart Example START statement1 statement2 statement3 statement4 END

1 nd Semester if statement flowchart statement1 if (condition) statement2; //true statement2; //true else { statement3; //false statement3; //false} statement4; true false CONDITION START statement1 statement2 statement3 statement4

1 nd Semester Quiz2 f(x) = 2x+10, x ≤ 5 x 2 +10, 5 < x ≤ 20 x 3 +10, x > 20 double fx = 0; double x = double.Parse(Console.ReadLine()); if ( ) fx = 2*x + 10; fx = 2*x + 10; else if ( ) fx = x*x + 10; fx = x*x + 10; else else fx = x*x*x + 10; fx = x*x*x + 10; Console.WriteLine(“f(x) = {0}”, fx);  Fill blanks in the program.  Write the program flowchart.

1 nd Semester Summary  Boolean Expression  Selection Statements if...else... Statement switch-case Statement if…else… Selection Problems switch

1 nd Semester Exercise1 (Homework) Ex1 Please input month: 5 Your month has 31 days. Input: month number (0-12) Output: #day in that month Ex2 Please input month: 2 Your month has 28 days. Try to use both if and case !