1. Module5 Looping Techniques: Part 2
Thanawin Rakthanmanon
Create by: Aphirak Jansang
Computer Engineering Department
Kasetsart University, Bangkok THAILAND

2. Switch-case example <expression> must be int, char, string
review
Switch-case example
<expression> must be int, char, string
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); :
default:
Console.Write("Try again"); }
int day_num;
day_num=
int.Parse(Console.ReadLine());
switch(day_num ) {
case 1:
Console.Write ("Sunday");
break;
case 2:
console.Write("Monday"); :
default :
Console.Write(“Try again"); }
<expression>

3. Switch-case example (continue)
review
Switch-case example (continue)
<expression> must be int, char, string
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); :
default:
Console.Write("Try again"); }
<expression>

4. Flowchart of Switch-case
review
Flowchart of Switch-case
int day_num;
day_num=
int.Parse(Console.ReadLine());
switch(day_num ) {
case 1:
Console.Write ("Sunday");
break;
case 2:
console.Write("Monday"); :
default :
Console.Write(“Try again"); }
label
(day_num)
label=1
statement1
(day_num=1)
label=2
statement2
(day_num=2)
label=3
statement3
(day_num=3) :
default
statement n

5. Looping or Iteration in C#
while
Iteration
for
foreach
do…while

6. Outline
do…while statement
for statement

7. while statement
while (condition)
statement;

8. do…while statement For Single Statement do { statement;
} while (condition);
For Multiple Statements do {
statement-1;
statement-2; .
statement-N;
} while (condition);

9. Sentinel Loops: example
static void Main() {
int N, SUM;
SUM = 0;
N = 0;
Console.Write(”Enter number or -1 to quit”);
N = int.Parse(Console.ReadLine());
while (N != -1) {
SUM = SUM+N; }
Console.WriteLine(“The sum is {0}.”, SUM);
1st Time (redundant part)

10. Sentinel Loops: do…while Version
static void Main() {
int N, SUM;
SUM = 0;
N = 0; do {
Console.Write(”Enter number or -1 to quit”);
N = int.Parse(Console.ReadLine());
if (N!= -1)
SUM = SUM+N;
} while (N != -1);
Console.WriteLine(”The sum is {0}.”, SUM); }

11. Factorial Number: C# Program
review
Factorial Number: C# Program
QUIZ1
N! = N * (N-1) * (N-2) * (N-3) *...* 1
Example 5! = 5*4*3*2*1
static void Main() {
int N, FACT=1;
FACT = 1;
Console.Write(”Please input number: ”);
N = int.Parse(Console.ReadLine());
while ( ?????? ) {
FACT = ?????? ;
???? ; };
Console.WriteLine(”The factorial is {0}.”,FACT); }
Find N!
N > 0
FACT * N
N--

12. Outline
do…while statement
for statement

13. for statement For Single Statement For Multiple Statements
for ( [initializers]; [expression]; [iterators] )
statement;
For Multiple Statements
for ( [initializers]; [expression]; [iterators] ) {
statement-1;
statement-2; .
statement-N; }

14. for statement k = ? for ( [initializers]; [expression]; [iterators] )
START
END
expression
true
false
Statement
iterators
initializers
for ( [initializers]; [expression]; [iterators] )
statement;
static void Main() {
int k;
for (k = 0; k <= 3; k++)
Console.Write("A ");
Console.Write(k); }
Example of for statement
k = ?
A A A A 4

15. Display 1 to 5 on screen while version for version
static void Main() {
int i;
i = 1;
while (i <= 5) {
Console.WriteLine(“{0}”, i);
i++; }
while version
static void Main() {
int i;
for (i=1; i<=5; i++) {
Console.WriteLine(“{0}”, i); }
for version

16. Problem #1 – Display 10 stars
START
END
expression
true
false
Statement
iterators
initializers
**********
static void Main() {
int i=0;
for ( ; ; )
Console.Write(”*”); }
i=0
i = 0
i < 10
i++
i<10
write(“*”)
i++
How to display N stars?

17. Problem #1: Find QUIZ2 i2 static void Main() { int N=0, SUM=0, i=0;5 i2
= 1*1 + 2*2 + 3*3 + 4*4 + 5*5
static void Main() {
int N=0, SUM=0, i=0;
Console.Write(”Please input number: ”);
N = int.Parse(Console.ReadLine());
for ( ????? ; ????? ; ????? )
SUM = SUM + ???? ;
Console.WriteLine(”SUM = {0}”, SUM); }
i = 1
i <= N
i++
i*i

18. Problem #3 – Display 4x3 stars
****
static void Main() {
int N=0, M=0;
for ( ; ; ) {
for ( ; ; ) {
Console.Write(”*”); }
Console.WriteLine();
M = 0
M < 3
M++
N = 0
N < 4
N++
How to display NxN stars?

19. Problem #4 – Triangle shape#1
*** ** *
static void Main() {
int N=0, M=0;
for ( ; ; ) {
for ( ; ; ) {
Console.Write(”*”); }
Console.WriteLine();
M = 3
M > 0
M--
N = 0
N < M
N++

20. Problem #5: Find 2n QUIZ3 static void Main() { int N=0, SUM=1, i=1;
Console.Write(”Please input number: ”);
N = int.Parse(Console.ReadLine());
while (i<=N){
SUM = SUM*2;
i++; }
Console.WriteLine(”SUM = {0}”, SUM);
for ( ; ; )
SUM = SUM * 2;
i = 1
i <= N
i++