Loops Counting down from N to 1 in assembly we used JUMP statements to repeat previous instructions thus looping READ LOOP: WRITE SUB decrement JPOSLOOP HALT decrement :1

Do Loops Stopping/looping condition but not sure how many iterations good with flags (or sentinels)‏ Come in two forms Do While --- LOOPING CONDITION Dim InputNum As Single InputNum=inputbox(“Enter a number to print, 0 to stop”)‏ Do While InputNum<>0 picResults.Print InputNum InputNum=inputbox(“Enter a number to print, 0 to stop”)‏ Loop What would happen if I don’t read input again from user inside loop? Do Until --- EXIT CONDIITON Dim InputNum As Single InputNum=inputbox(“Enter a number to print, 0 to stop”)‏ Do Until InputNum=0 picResults.Print InputNum InputNum=inputbox(“Enter a number to print, 0 to stop”)‏ Loop Print even numbers between 2 and 100 in a picturebox

Do Loops Dim counter As Integer counter=2 Do While counter <=100 picResults.Print counter counter = counter +2 Loop Dim counter As Integer counter=2 Do Until counter >100 picResults.Print counter counter = counter +2 Loop Same initialization phase for loop variable (Outside loop)‏ Syntactically different exit conditions (Semantically the same)‏ Opposite to one another Same action (Loop body: Do … Loop)‏

Do Loops Program to compute the average for any class exam at CSBSJU Enter any number of grades When the flag (-1) is provided end of input and print average Algorithm + program Show program

Do Loops Program to get the average of any number of grades (enter -1 to exit)‏ Sum = 0, count=0, average=0 grade=input by user While grade <> -1 Add grade to sum Add 1 to count Enter another grade Divide sum by count to obtain the average Print average

Do Loops Private Sub cmdAverageButton_Click()‏ ‘program to compute the average exam score Dim count As Integer Dim grade As Single, sum As Single, avg As Single grade = InputBox (“Enter the first exam score:”, ”Exam Scores”)‏ Do While grade <> -1 sum = sum + grade count = count + 1 grade = InputBox(“Enter another score Type -1 to end.”, “Exam Scores”)‏ Loop avg = sum/count MsgBox “The average is: ” & FormatNumber(avg)‏ End Sub

For Next Loops When we know how many times we need to repeat the loop With a consistent increase or decrease  For Next Loops are better Display values between 1 to 5 (vs. until user inputs -1)‏ Dim CTR As Integer For CTR = 1 to 5 picResults.Print CTR Next CTR After every loop, the loop counter is incremented by 1 (default)‏ Initialization: CTR=1 Exit Condition: CTR>5 Action: Results.Print CTR Combines the initialization and exit conditions into one line Previously initialization was done before loop

For Next Loops After every loop, the loop counter is incremented by 1 (default)‏ Can be changed by specifying steps (display even numbers from 2 to 100)‏ For CTR = 2 to 100 Step 2 picResults.Print CTR Next CTR Can be positive or negative (display even numbers from 100 to 2)‏ For CTR = 100 to 2 Step -2 picResults.Print CTR Next CTR

For Next Loops The steps don’t have to be integers For CTR = 1 to 3 Step.5 picResults.Print CTR Next CTR Suppose we want to display all even numbers between 2 and another number specified by the user Dim CTR as Integer, N As Integer N = txtEndBox.Text For CTR = 2 to N Step 2 picResults.Print CTR Next CTR Design a VB program that displays in a picture box the first N multiples of an input integer