=====Alternative FOR NEXT behaviour=====

//by Richard Russell, July 2007//\\ \\  Although the **FOR**...**NEXT** loop is fundamental to all versions of BASIC, dialects differ in its detailed implementation. In **BBC BASIC** FOR...NEXT loops have the following properties:

  * The body of the loop is always executed at least once, irrespective of the values specified in the FOR statement.
  * On exit from the loop the loop variable has a value //greater than// (for a positive STEP) the TO value specified in the FOR statement, i.e. one more STEP has taken place.

The following examples illustrate this behaviour:\\
<code bb4w>
        FOR i% = 1 TO 0
          PRINT i%
        NEXT i%
</code>
<code bb4w>
        FOR i% = 1 TO 10
        NEXT i%
        PRINT i%
</code>
The first loop prints **1**, even though the 'finish' value is less than the 'start' value.

The second loop prints **11**, which is one more than the 'finish' value.

On occasion you may wish to emulate the behaviour of a different BASIC dialect, for example when porting a program to BBC BASIC. One convenient way of doing that is to use the [[http://www.bbcbasic.co.uk/bbcwin/manual/bbcwin5.html#exit|EXIT FOR]] statement.

Some BASIC dialects //do not execute the FOR loop at all// if the initial conditions aren't met, i.e. the 'finish' value is less than the 'start' value (with a positive STEP). To emulate that behaviour use code similar to the following:\\ 
<code bb4w>
        FOR loopvar = start TO finish
          IF loopvar > finish THEN EXIT FOR
          REM Body of loop here
        NEXT loopvar
</code>
Some BASIC dialects exit the loop //with the loop variable equal to the 'finish' value//. To emulate that behaviour use code similar to the following:\\
<code bb4w>
        FOR loopvar = start TO finish
          REM Body of loop here
          IF loopvar >= finish THEN EXIT FOR
        NEXT loopvar
</code>
Of course you can combine both behaviours if you wish:\\ 
<code bb4w>
        FOR loopvar = start TO finish
          IF loopvar > finish THEN EXIT FOR
          REM Body of loop here
          IF loopvar >= finish THEN EXIT FOR
        NEXT loopvar
</code>
In all cases if the STEP is negative you need to reverse the comparisons:\\ 
<code bb4w>
        FOR loopvar = start TO finish STEP -delta
          IF loopvar < finish THEN EXIT FOR
          REM Body of loop here
          IF loopvar <= finish THEN EXIT FOR
        NEXT loopvar
</code>