Iteration
Using loops
in VB.NET
1

Loop structures
These are used when we want lines of code
to be executed many times
We might want it to run a set number of
times.
We may need to check if various conditions
have been met.
There are loops for all occasions and
programmers have their “favourites”!
2

Fixed Loop structures
If we want the loop to run a fixed number
of times, we use a For…..Next loop
This will use a variable as a counter
Syntax:
For first value To last value
Line of code to execute
Next value
3

For...Next example
4

Conditional Loop Structures
If we want the loop to repeat until a
condition changes (at runtime).
Use While …. End While to check the
condition before running loop
Syntax:
While condition = true
Line of code execute
End While
5

While…End While example
6

Conditional Loop Structures
Use Do…. Loop to run until a condition
becomes true
This code will run at least once
 Beware! It is possible to create loops that
carry on to infinity. Press Ctrl + Break to
stop, but you may lose some unsaved work
Syntax:
Do
Line of code to execute
Loop Until condition = true
7

Do… Loop Until example
8

Programming terms
When we need to repeat a set of
instructions, we have 3 options:
 For….Next - runs for fixed number of loops
 While…End While - runs while condition is true
 Do…Loop Until - runs until condition becomes
true
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