Repetition Statements Repeating an Action A specified number

Repetition Statements �Repeating an Action �A specified number of times �While a Condition is True �Until a Condition is True

3 Requirements for a Successful Loop �Initialize a Loop Control Variable �Test the Loop Control Variable against an Exit Condition �Update the Loop Control Variable �Must be approaching exit criteria

Counted / For Loop �Specified Number of Times �Syntax: For loop. Variable = start To End [Step. Value] Statements Next [loop. Variable] �[ ] means optional

Example For counter = 1 to 10 Step 1 msg. Box (“The current number is: “ & counter) Next

Try It �Write a program that uses a counted/for loop to read in a 5 numbers (using an input. Box) and display their average in a label.

Try it Again �Write a program using a counted/for loop that will add the numbers from 1 – 50 and display the output in a label. �Write a program using a counted/for loop that will add the odd numbers from 1 – 50 and display the output in a label.

While Loops �Continue Looping While a Condition is True �Syntax: Do While (condition statement) statements Loop

Pre-Test Loop �In a While Loop the Loop Exit condition is tested before the program enters the loop �Pre-Test Loop �If Condition is False, the Loop code may never execute Minimum number of executions of loop is 0

Example Do While (number <=10) Msg. Box (“The current number is: “ & number) number = number + 1 Loop

Try It �Write a program to require the user to enter a correct password (“Friday”). When they enter the correct password the program will display “Have a Great Week-end”.

Try it Again �Write a program that will calculate the number of years it will take for a given input deposit amount to increase to a million dollars at 6% annual interest. �Test $100, 000 should take 40 years

Do Until Loop � Continues Executing Until a Condition is True � Syntax Do statements Loop Until (condition)

Post Test Loop � In a Do. . Until Loop the loop checks Exit Condition After the Loop Executes � Post Test Loop � Minimum Number of Executions of Loop is 1

Example Dim str. Password Do str. Password = Input. Box (“Enter Password”) Loop Until (str. Password = “Friday”)

Try It � Note: All Loops can be written as Do While Loops � Practice this example using a D 0 Until Loop � Write a program that reads in a list of positive integers from the user until the user enters the value of -1 (a sentinel value – exit value). At that time the program should display the largest value in the input list.

Review of Loops � 3 Requirements for Successful Loop � Initialize a Loop Control Variable � Test the Loop Control Variable against an Exit Condition � Update the Loop Control Variables � 3 Types of Loops � Counted Loop – executes a specific number of times � While Loop – Pre-test loop � Do Until Loop – Post-test loop � ALL Loops can be written as While Loops