3.2.2 - Count-controlled iteration (VB.NET)

Choosing the repetition count

A count-controlled loop repeats a body a number of times determined when the loop begins.

If a quiz contains four rounds, a For loop can display each round number:

For round As Integer = 1 To 4
    Console.WriteLine("Round " & round)
Next

The body executes for 1, 2, 3 and 4. VB.NET's To endpoint is inclusive. The default step is +1; For number As Integer = 6 To 2 Step -2 visits 6, 4, 2. A positive-step loop whose start exceeds its end performs no iterations. For i As Integer = 1 To 0 therefore has an empty body run.

Iteration combines with sequence inside its body and selection where a repeated decision is needed. Place an instruction inside the loop when it must happen for each round, and after Next when it must happen once after all rounds. Do not modify the loop counter yourself to simulate extra updates; Next already advances it. Use a separately declared result if you need data after the loop; do not rely on counter values after a loop, especially when translating supplied AQA pseudocode.

Tracing counters and accumulators

An accumulator stores a result built across successive iterations rather than replacing it with the last input.

Dim total As Integer = 0
For round As Integer = 1 To 3
    Dim score As Integer = CInt(Console.ReadLine())
    total = total + score
Next
Console.WriteLine(total)

With scores 4, 7, 2, trace the state after each addition: