Loops ISYS 350

A Box of Chocolate Analogy Repeat this process until box is empty: Take one chocolate from the box Eat the chocolate Box has more chocolate? Or Repeat this process until you are full: Am I full? Eat three chocolates

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

Compute the maximum of a list of numbers: Example: 5, 2, 10, 8, 4 Process: Determine Max Set Max to the first number (Max = first number) 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

Three Types of Loops while loop do loop for loop

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

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

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

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

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

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; }

Accumulator Find the sum of all numbers between 1 and N. Method 1: int N, Sum, Counter = 1; N = int.Parse(textBox1.Text); Sum = 0; while (Counter <= N) { Sum += Counter; ++Counter; } MessageBox.Show(Sum.ToString());

Accumulator Method 2 int N, Sum; N= int.Parse(textBox1.Text); Sum = 0; while (N > 0) { Sum += N; N -= 1; } MessageBox.Show(Sum.ToString());

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 Framework 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());

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());

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());

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());

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; }

Enter Loan and Term in textboxes, then display monthly pay for rates from 0.5% to 6% with a step of 0.5% in a ListBox double loan, rate, term, payment; loan = double.Parse(textBox1.Text); term = double.Parse(textBox2.Text); rate = 0.005; while (rate <= .06) { payment = Financial.Pmt(rate / 12, term * 12, -loan); listBox1.Items.Add(“Rate = " + rate.ToString(“p”) + " Payment is: " + payment.ToString("c")); rate += .005; }

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

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”); }

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--)

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());

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")); }

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")); }

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());