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11nd Semester 2007
ModuleModule33 Selection StatementSelection Statement
Thanawin RakthanmanonEmail: [email protected]
Create by: Aphirak JansangComputer Engineering Department
Kasetsart University, Bangkok THAILAND
21nd Semester 2007
Outline
Boolean expression ifif statement nested ifnested if statement switch caseswitch case statement
31nd Semester 2007
Boolean Expression Operators
Comparison Equal ==== Not equal !=!= Less << Greater >> Less than or equal to <=<= Greater than or equal to >=>=
Boolean And &&&& Or |||| Not !!
41nd Semester 2007
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 //true if X is the answeranswer
(Y%2 == 0) //true if Y is even//true if Y is even
OROR
(Y%2 != 1) //true if Y is even//true if Y is even
51nd Semester 2007
Example: Boolean Expressions
double x = 4.0; Expression Valuex < 5.0 ___________x > 5.0 ___________x <= 5.0 ___________5.0 == x ___________x != 5.0 ___________
truefalsetruefalsetrue
61nd Semester 2007
Outline
Boolean expression ifif statement nested ifnested if statement switch caseswitch case statement
71nd Semester 2007
if statement
Execute the specific statement when the ”condition””condition” becomes truetrue
Syntax:
if if (condition)(condition)
statement;statement; //true//true
if if (condition)(condition) {{
statement1; statement1; //true//true
statement2; statement2; //true//true
}}
81nd Semester 2007
if statement example
BMI (Body Mass Index)
BMI Weight 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 KilogramsWeight in Kilograms
(Height in Meters) X (Height in Meters)(Height in Meters) X (Height in Meters)
91nd Semester 2007
if…else… statement
If conditioncondition is truetrue execute statement1statement1
If conditioncondition is falsefalse execute statement2statement2
Syntax:if if (condition)(condition)
statement1; statement1; //true//true
elseelse
statement2; statement2; ////falsefalse
if if (condition)(condition)
statement1; statement1; //true//true
elseelse { {
statement2; statement2; ////falsefalse
statement3; statement3; ////falsefalse
}}
101nd Semester 2007
if…else… statement example Question
Value in variable N is Odd or Even Number?
Value in N OutputEven Number It’s even number.
Odd Number It’s odd number.
if if (___________________)(___________________)
Console.WriteLine(“It’s even Console.WriteLine(“It’s even number.”);number.”);
elseelse
Console.WriteLine(“It’s odd Console.WriteLine(“It’s odd number.”);number.”);
111nd Semester 2007
Quiz Fill the following blank
What x, y, z are called ?
Rewrite this sentence
10110102 = ?
if if (___________________)(___________________)
Console.WriteLine(“It’s even Console.WriteLine(“It’s even number.”);number.”);
elseelse
Console.WriteLine(“It’s odd Console.WriteLine(“It’s odd number.”);number.”);
xx11xx22 zzyy
int Width,High;int Width,High;Width=10;Width=10;High=5;High=5;
int int ______________;;int int ______________;;
Hint: 26 + 24 + 23 + 21 = ?
X%2 == 0
121nd Semester 2007
Outline
Boolean expression ifif statement nested ifnested if statement switch caseswitch case statement
131nd Semester 2007
Nested if statement
int N;int N;N = int.Parse(Console.ReadLine());N = int.Parse(Console.ReadLine());
if (N >= 0) if (N >= 0) {{ if (N==0)if (N==0) Console.WriteLine(“N is zero number”);Console.WriteLine(“N is zero number”); elseelse Console.WriteLine(“N is positive number”); Console.WriteLine(“N is positive number”); }}else else Console.WriteLine(“N is negative number”);Console.WriteLine(“N is negative number”);
if#1if#1
if#2if#2
141nd Semester 2007
Nested IF Overview
if#1if#1if#2if#2
if#3if#3
if#1if#1
if#2if#2
if#3if#3
else#1else#1=
151nd Semester 2007
Nested if statement
f(x) =f(x) =
2x+10, x ≤ 52x+10, x ≤ 5
xx22+10, 5 < x ≤ 20+10, 5 < x ≤ 20
xx33+10, x > 20+10, x > 20
Range Boolean Expression
x ≤ 5x ≤ 5 (x (x <<= 5)= 5)
5 < x ≤ 205 < x ≤ 20 ((5 < x) && (x <= 20))((5 < x) && (x <= 20))
x > 20x > 20 (x > 20)(x > 20)
161nd Semester 2007
Nested if statement
f(x) =f(x) =2x+10, x ≤ 52x+10, x ≤ 5xx22+10, 5 < x ≤ 20+10, 5 < x ≤ 20xx33+10, x > 20+10, x > 20
double fx = 0;double fx = 0;double x = double.Parse(Console.ReadLine());double x = double.Parse(Console.ReadLine());
#1 #1 if ( )if ( )#2#2 fx = 2*x + 10; fx = 2*x + 10;#3 #3 else if ( )else if ( )#4 #4 fx = x*x + 10; fx = x*x + 10;#5#5 else else #6#6 fx = x*x*x + 10; fx = x*x*x + 10;#7#7#8 #8 Console.WriteLine(“f(x) = {0}”, fx);Console.WriteLine(“f(x) = {0}”, fx);
X <= 5
5 < x <= 20
171nd Semester 2007
Outline
Boolean expression ifif statement nested ifnested if statement switch caseswitch case statement
181nd Semester 2007
switch…case statement For selecting a statement where its label
corresponds to the value of the switch expression.
switch (<expression><expression>){ case <constant-<constant-expression>expression> : <statements>;<statements>; break;break; [default: <statements>;<statements>; break;break;]}<expression><expression> must be int, char, string must be int, char, string
191nd Semester 2007
Example: switch-case (1)
int day_num;
day name
1 Sunday
2 Monday
3 Tuesday
4 Wednesday
5 Thursday
6 Friday
7 Saturday
int day_num;
Console.Write("Input the day"); day_num = int.Parse(Console.ReadLine());
switch(day_numday_num) {case 1:1: Console.Write ("Today is Sunday"); break;
case 2:2: Console.Write("Today is Monday"); break; : default :: Console.Write ("I don’t know"); break;}
<expression><expression>
<constant-expression><constant-expression>
201nd Semester 2007
Example: switch-case (2)
int month;
month
1 January
2 February
3 March
4 April
… …..
… …..
12 December
int month;
Console.Write("Input Month"); month = int.Parse(Console.ReadLine());
switch(monthmonth) {case 1:1: case 3:3: case 5:5: Console.Write("This month has 31day"); break; case 4:4: case 6:6: Console.Write("This month has 30day"); break; default :: Console.Write ("Input again"); break;}
211nd Semester 2007
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;}
<expression><expression> must be must be int, char, stringint, 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><expression>
iintnt version versionchar versionchar version
<<constant-constant-expression>expression>
221nd Semester 2007
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;}
<expression><expression> must be must be int, char, stringint, char, string
string versionstring version
<expression><expression>
<<constant-constant-expression>expression>
231nd Semester 2007
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 defaultswitch version with default
<<constant-constant-expression>expression>
<expression><expression>must be must be int, char, stringint, 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 versionif else version
switch (a) { case 1 : case 2 : Console.WriteLine("Hi"); break;}
switch version without defaultswitch version without default
241nd Semester 2007
Flowchart Symbols Overview
Graphical representation
Terminator
Process
Input/output
Condition
Connector
Flow line
251nd Semester 2007
Program Flowchart Example
START
statement1statement1
statement2statement2
statement3statement3
statement4statement4
END
261nd Semester 2007
if statement flowchart
statement1statement1
if if (condition)(condition)
statementstatement22; ; ////truetrue
elseelse { {
statementstatement33; ; ////falsefalse
}}
statementstatement44; ;
truetruefalsefalse
CONDITIONCONDITION
START
statement1statement1
statement2statement2statement3statement3
statement4statement4
271nd Semester 2007
Quiz2
f(x) =f(x) =2x+10, x ≤ 52x+10, x ≤ 5
xx22+10, 5 < x ≤ 20+10, 5 < x ≤ 20xx33+10, x > +10, x > 20 20double fx = 0;double fx = 0;
double x = double.Parse(Console.ReadLine());double x = double.Parse(Console.ReadLine());
if ( )if ( ) fx = 2*x + 10;fx = 2*x + 10;else if ( )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);Console.WriteLine(“f(x) = {0}”, fx);
Fill blanks in the program. Write the program flowchart.
281nd Semester 2007
Summary
Boolean Expression Selection Statements
if...else... Statement switch-case Statement
if…else…if…else…
Selection ProblemsSelection Problems
switchswitch
291nd Semester 2007
Exercise1 (Homework)
Ex1Please input month: 5Your month has 31 days.
Input: month number (0-12)
Output: #day in that month
Ex2Please input month: 2Your month has 28 days.
Try to use both if and case !
