1. Loops
ISYS 350

2. Compute the sum of a list of numbers: Example: 5, 2, 10, 8, 4
Process:
Sum= 0
Get a number from the list
Sum = Sum + the number
Repeat this part until no more data
Show the value of Sum

3. Compute the maximum of a list of numbers: Example: 5, 2, 10, 8, 4
Process:
Max = a very small number (such as )
Get a number from the list
If the number is greater than Max Then Max = the number
Repeat this part until no more data
Show the value of Max

4. Three Types of Loops
while loop
do loop
for loop

5. The while Loop
The while loop causes a statement or set of statements to repeat as long as a Boolean expression is true
The simple logic is: While a Boolean expression is true, do some task
A while loop has two parts:
A Boolean expression that is tested for a true or false value
A statement or set of statements
that is repeated a long as the
Boolean expression is true
Boolean
Expression
Statement(s)
True
False

6. Structure of a while Loop
In C#, the generic format of a while loop is:
while (BooleanExpression) {
Statements; }
The first line is called the while clause
Statements inside the curly braces are the body of the loop
When a while loop executes, the Boolean expression is tested. If true, the statements are executed
Each time the loop executes its statement or statements, we say the loop is iterating, or performing an iteration

7. An Infinite Loop
while (1 > 0) {
MessageBox.Show("Looping"); }

8. An Infinite Loop that plays beep sound
To play beep, we need System.Media namespace:
using System.Media;
while (1 > 0) {
SystemSounds.Beep.Play(); }

9. Using a Counter to Control the Loop
int counter = 0;
while (counter<5) {
MessageBox.Show(counter.ToString());
++counter;
//counter++; }

10. Using a Flag Boolean continueFlag = true; while (continueFlag) {
SystemSounds.Beep.Play();
if (MessageBox.Show("Do you want to continuue? ", "Continue?", MessageBoxButtons.YesNo) == DialogResult.No)
continueFlag = false; }

11. Interactive Input using VB’s InputBox Statement
Add a reference to Microsoft Visual Baisc:
1. From the Solution Explorer, right-click the References node, then click Add Reference
2. From the .Net tab, select Microsoft Visual Baisc
3. Add this code to the form:
using Microsoft.VisualBasic;
Example of using InputBox:
int myint;
myint= int.Parse(Interaction.InputBox("enter a number:"));
MessageBox.Show(myint.ToString());

12. Accumulator Find the sum of all numbers between 1 and N. Method 1:
int N, Sum, Counter = 1;
N = int.Parse(Interaction.InputBox("enter an integer:"));
Sum = 0;
while (Counter <= N) {
Sum += Counter;
++Counter; }
MessageBox.Show(Sum.ToString());

13. Accumulator Method 2 int N, Sum;
N= int.Parse(Interaction.InputBox("enter a integer:"));
Sum = 0;
while (N > 0) {
Sum += N;
N -= 1; }
MessageBox.Show(Sum.ToString());

14. While Loop Example N Factorial, N!
int N, NFact, Counter = 1;
N = int.Parse(Interaction.InputBox("enter a integer:"));
NFact = 1;
while (Counter <= N) {
NFact *= Counter;
++Counter; }
MessageBox.Show(NFact.ToString());

15. Enter Loan and Rate in textboxes, then display monthly pay for terms from 5 to 40 with a step of 5 in a ListBox
double loan, rate, term, payment;
loan = double.Parse(textBox1.Text);
rate = double.Parse(textBox2.Text);
term = 5;
while (term <= 40) {
payment = Financial.Pmt(rate / 12, term * 12, -loan);
listBox1.Items.Add("Term = " + term.ToString() + " Payment is: " + payment.ToString("c"));
term += 5; }

16. The for Loop
The for loop is specially designed for situations requiring a counter variable to control the number of times that a loop iterates
You must specify three actions:
Initialization: a one-time expression that defines the initial value of the counter
Test: A Boolean expression to be tested. If true, the loop iterates.
Update: increase or decrease the value of the counter
A generic form is:
for (initializationExpress; testExpression; updateExpression)
{ }
The for loop is a pretest loop

17. Sample Code
int count;
for (count = 1; count <= 5; count++) {
MessageBox.Show(“Hello”); }
The initialization expression assign 1 to the count variable
The expression count <=5 is tested. If true, continue to display the message.
The update expression add 1 to the count variable
Start the loop over
// declare count variable in initialization expression
for (int count = 1; count <= 5; count++) {
MessageBox.Show(“Hello”); }

18. Other Forms of Update Expression
In the update expression, the counter variable is typically incremented by 1. But, this is not a requirement.
//increment by 10
for (int count = 0; count <=100; count += 10) {
MessageBox.Show(count.ToString()); }
You can decrement the counter variable to make it count backward
//counting backward
for (int count = 10; count >=0; count--)

19. Accumulator Find the sum of all numbers between 1 and N. Mrthod 1:
int N, Sum, Counter;
N = int.Parse(Interaction.InputBox("enter an integer:"));
Sum = 0;
for (Counter = 1; Counter <= N;Counter++ ) {
Sum += Counter; }
MessageBox.Show(Sum.ToString());
Method 2:
int N, Sum, Counter;
N = int.Parse(Interaction.InputBox("enter an integer:"));
Sum = 0;
for (Counter = N; Counter>0;Counter-- ) {
Sum += Counter; }
MessageBox.Show(Sum.ToString());

20. Enter Loan and Rate in textboxes, then display monthly pay for terms from 5 to 40 with a step of 5 in a ListBox
double loan, rate, term, payment;
loan = double.Parse(textBox1.Text);
rate = double.Parse(textBox2.Text);
for (term = 5; term <= 40;term+=5 ) {
payment = Financial.Pmt(rate / 12, term * 12, -loan);
listBox1.Items.Add("Term = " + term.ToString() + " Payment is: " + payment.ToString("c")); }

21. Increment smaller than 1: Enter Loan and Term in textboxes, then display monthly pay for rates from 3% to 10% with a step of .5% in a ListBox
double loan, rate, term, payment;
loan = double.Parse(textBox1.Text);
term = double.Parse(textBox2.Text);
for (rate = .03; rate <= .1;rate+=.005 ) {
payment = Financial.Pmt(rate / 12, term * 12, -loan);
listBox1.Items.Add("rate = " + rate.ToString("p") + " Payment is: " + payment.ToString("c")); }

22. © 2007, Mike Murach & Associates, Inc.
Find the Sum of All Even Numbers between 1 and N
int N, Sum, Counter;
N = int.Parse(Interaction.InputBox("enter an integer:"));
Sum = 0;
for (Counter = 1; Counter<=N;Counter++ ) {
if (Counter % 2 ==0)
Sum += Counter; }
MessageBox.Show(Sum.ToString());
Murach’s Java SE 6, C4
© 2007, Mike Murach & Associates, Inc.