ME 142Engineering Computation I

Loops

Key Concepts

Looping Basics

For… Next Statement

Do… Loop Statement

For Each… Next Statement

Looping Basics

Looping Basics

The term loop or looping refers to repeating a block of code multiple times.

Must be able to end loop – otherwise infinite loop!! Execute pre-determined number of times Execute until a condition is satisfied

For...Next Statement

For… Next Statement

The For… Next statement is used to repeatedly execute a block of statements a specified number of times.

For counter = start to end [Step stepsize]

[statements]

Next [counter]

For… Next Example

For I = 1 to 5

Cells(I,1) = I

Next I

For… Next Example

For I = 1 to 5

ActiveCell.Value = I

ActiveCell.Offset(1,0).Select

Next I

For… Next ExampleSub demo()

‘Computes average of cells A1:A5

Total = 0

For i = 1 To 5

Total = Total + Cells(i, 1)

Next I

Average = Total / 5

MsgBox "Average = " & Average

End Sub

Example Problem Create a factorial function using For Next

loops. Pass the function the number whose factorial is to be computed. After computing the factorial, the results should be displayed in the cell from which the function is called.

Use the factorial function you created to compute the factorials for the integers 1 through 10.

Example Problem SolnFunction factorial(n)

'computes the factorial of a number

Total = 1

For i = 1 To n

Total = Total * i

Next i

factorial = Total

End Function

Do...Loop Statement

Do… Loop Statement

The Do… Loop statement is used to repeatedly execute a block of statements until a specified condition is met. Conditions are tested using While and Until at either the beginning or end of the loop.

Do… Loop StatementDo [While condition]

[statements]

Loop

Do

[statements]

Loop [While condition]

Do [Until condition]

[statements]

Loop

Do

[statements]

Loop [Until condition]

Do

[statements]

Loop

Do… Loop Examplex = 1

Do

Cells(x,1) = x

x = x + 1

Loop Until x = 5

x = 1

Do Until x =5

Cells(x,1) = x

x = x + 1

Loop

Do… Loop Examplex = 10

Do

Cells(x,1) = x

x = x + 1

Loop Until x = 5

Use Ctrl+Break or Esc to stop execution of infinite loop

Do… Loop Examplex = 10

Do

Cells(x,1) = x

x = x + 1

Loop Until x> = 5

x = 10

Do Until x >=5

Cells(x,1) = x

x = x + 1

Loop

Example Problem Create a factorial function using Do loops.

Pass the function the number whose factorial is to be computed. After computing the factorial, the results should be displayed in the cell from which the function is called.

Use the factorial function you created to compute the factorials for the integers 1 through 10.

Example Problem SolnFunction factorial(n)'computes the factorial of a number

Total = 1I = 1

Do While I <= n Total = Total * I I = I + 1Loop

factorial = Total

End Function

For Each...Next Statement

For Each… Next StatementThe For Each…Next statement is used to loop through

each object in a collection of objects. An example of this would be to loop through each of the cells in a range of cells.

For Each element In collection

[statements]

Next [element]

For Each… Next ExampleFunction ForEachDemo(MyRange)

Total = 0

For Each Cell In MyRange

Total = Total + Cell.Value

Next Cell

ForEachDemo = Total

End Function

For Each… Next ExampleSub FillDemo()

‘Fill a selection with random numbers

For Each cell In Selection

cell.Value = Rnd

Next cell

End Sub

Review Questions

Review Question

What is the value of Count after the loop has finished executing:

Count=0For I = 1 to 5Count = Count + I

Next I

A.0

B.5

C.10

D.15

E.None of the above

Review Question

What is the value of Count after the loop has finished executing:

x=1Count=0DoCount = Count + xx = x + 1

Loop Until x = 5A.0B.5C.10D.15E.None of the above

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