SBasic language reference::For...Next statements

For...Next Statements
Repeats a group of statements a specified number of times.

Format:

   For counter = start To end [ Step step ]
      [ statements ]
   [ Exit For ]
      [ statements ]
   Next

Syntax:

counter
Required. Variable. The data type of counter is usually Integer but can be any elementary numeric type that supports the greater than or equal to (>=), less than or equal to (<=), and addition (+) operators.
start
Required. Expression. The initial value of counter. The start expression usually evaluates to type Integer but can evaluate to any numeric type.
end
Required. Expression. The final value of counter. The end expression usually evaluates to type Integer but can evaluate to any numeric type.
step
Optional. Expression. The amount by which counter is incremented each time through the loop. The step expression usually evaluates to type Integer but can evaluate to any numeric type. If not specified, step defaults to 1.
statements
Optional. One or more statements between For and Next that are executed the specified number of times.

Remarks:

1. If counter has not been declared outside this loop, you can declare it within the For statement.

2. The step argument can be either positive or negative.

3. The expressions start, end, and step are all evaluated only once, when the For statement is first encountered. They are not evaluated again, even if the loop statements change their constituent parts.

4. After the loop statements have executed, step is added to counter. At this point, the For statement again compares counter to end. As a result of this comparison, either the statements in the loop execute again, or the loop is terminated and execution continues with the statement following the Next statement.

5. Changing the value of counter while inside a loop can make it more difficult to read and debug your code.

6. The Exit For statement transfers control immediately to the statement following the Next statement. Any number of Exit For statements can be placed anywhere in the For...Next loop. Exit For is often used after evaluating some condition, for example with an If...Then...Else statement.

7. Loop executes if:
- step value is non zero
- start <= end and step > 0
- start > end and step < 0
Otherwise For statement is not executed.

8. You can nest For...Next loops by placing one loop within another. Each loop must have a unique counter variable. The following construction is correct:

     For I = 1 To 10
        For J = 1 To 10
           For K = 1 To 10
              ' Statements to operate with current values of I, J, and K.
           Next
        Next
     Next

Example:

     For I = 1 To 10
        For J = 1 To 10
           For K = 1 To 10

              Print "i=",i, ", j=",j, ", k=", k

              num = Rnd*100 ' lets exit from for randomly
              if num=50 then
                Print "Exiting from for..."
                Exit For 
              endif

           Next
        Next
     Next