Chapter 6 - VB 2005 by Schneider 1

SampleDim i As Integer

For i = 1 To 5

lstTable.Items.Add(i & " " & i ^ 2)

Next

The loop control variable, i, is • Initialized to 1• Tested against the stop value, 5• Incremented by 1 at the Next statement

Chapter 6 - VB 2005 by Schneider 2

For…Next Loop Syntax

Uthaisombut & Schneider 3

Set control variableto initial value

ExecuteStatementsin loop body

Incrementcontrol variable

Is control variable >terminating value?

Executestatements

following the loop

Yes

No

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Example 2

For index = 0 To n Step s

lstValues.Items.Add(index)

Next

Controlvariable

Startvalue

Stopvalue

Amountto add to

index

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Example with Negative StepDim j As Integer

For j = 10 To 1 Step -1

lstBox.Items.Add(j)

Next

lstBox.Items.Add("Blastoff")

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Declaration Inside For Statement

Dim i As Integer

For i = 1 To 5

lstTable.Items.Add(i & " " & i ^ 2)

Next

For i As Integer = 1 To 5

lstTable.Items.Add(i & " " & i ^ 2)

Next

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Nested For…Next Loops

Chapter 6 - VB 2005 by Schneider 8

For and Next Pairs

• For and Next statements must be paired.

• If one is missing, the automatic syntax checker will complain with a wavy underline and a message such as

“A ‘For’ must be paired with a ‘Next’.”

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Start, Stop, and Step values

• Consider a loop beginning with

For i As Integer = m To n Step s.

• The loop will be executed exactly once if m equals n no matter what value s has.

• The loop will not be executed at all if m is greater than n and s is positive,

or if m is less than n and s is negative.

Loop in Action

For i = 1 to 4

Picture1.print i * 2

Next

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Loop in ActionFor i = 1 to 4

Picture1.print i * 2

Next

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Value of i

Picture1 Output

Loop in ActionFor i = 1 to 4

Picture1.print i * 2

Next

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Value of i

1

Picture1 Output

2

Loop in ActionFor i = 1 to 4

Picture1.print i * 2

Next

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Value of i

2

Picture1 Output

2 4

Loop in ActionFor i = 1 to 4

Picture1.print i * 2

Next

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Value of i

3

Picture1 Output

2 4 6

Loop in ActionFor i = 1 to 4

Picture1.print i * 2

Next

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Value of i

4

Picture1 Output

2 4 6 8

Loop in Action

For i = 1 to 4

x = i mod 5

storeMe(i)

Picture1.print i * 2

Next

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