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Loops. Counting down from N to 1 in assembly we used JUMP statements to repeat previous instructions thus looping. READ LOOP: WRITE SUB decrement JPOS LOOP HALT decrement :1. Do Loops. Stopping/looping condition but not sure how many iterations
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Loops • Counting down from N to 1 in assembly we used JUMP statements to repeat previous instructions thus looping • READ • LOOP: WRITE • SUB decrement • JPOS LOOP • 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 Whilecounter <=100 • picResults.Print counter • counter = counter +2 • Loop • Dim counter As Integer • counter=2 • Do Untilcounter >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 consistentincrease 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
