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alternative_20for_20next_20behaviour [2018/03/31 13:19] – external edit 127.0.0.1alternative_20for_20next_20behaviour [2024/01/05 00:22] (current) – external edit 127.0.0.1
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 =====Alternative FOR NEXT behaviour===== =====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:\\ \\ +//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.   * 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.   * 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:\\ \\ + 
 +The following examples illustrate this behaviour:\\ 
 +<code bb4w>
         FOR i% = 1 TO 0         FOR i% = 1 TO 0
           PRINT i%           PRINT i%
         NEXT i%         NEXT i%
 +</code> 
 +<code bb4w>
         FOR i% = 1 TO 10         FOR i% = 1 TO 10
         NEXT i%         NEXT i%
         PRINT i%         PRINT i%
-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 available in //BBC BASIC for Windows// version 5.60a or later.\\ \\  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> 
 +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         FOR loopvar = start TO finish
           IF loopvar > finish THEN EXIT FOR           IF loopvar > finish THEN EXIT FOR
           REM Body of loop here           REM Body of loop here
         NEXT loopvar         NEXT loopvar
-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> 
 +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         FOR loopvar = start TO finish
           REM Body of loop here           REM Body of loop here
           IF loopvar >= finish THEN EXIT FOR           IF loopvar >= finish THEN EXIT FOR
         NEXT loopvar         NEXT loopvar
-Of course you can combine both behaviours if you wish:\\ \\ +</code> 
 +Of course you can combine both behaviours if you wish:\\  
 +<code bb4w>
         FOR loopvar = start TO finish         FOR loopvar = start TO finish
           IF loopvar > finish THEN EXIT FOR           IF loopvar > finish THEN EXIT FOR
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           IF loopvar >= finish THEN EXIT FOR           IF loopvar >= finish THEN EXIT FOR
         NEXT loopvar         NEXT loopvar
-In all cases if the STEP is negative you need to reverse the comparisons:\\ \\ +</code> 
 +In all cases if the STEP is negative you need to reverse the comparisons:\\  
 +<code bb4w>
         FOR loopvar = start TO finish STEP -delta         FOR loopvar = start TO finish STEP -delta
           IF loopvar < finish THEN EXIT FOR           IF loopvar < finish THEN EXIT FOR
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           IF loopvar <= finish THEN EXIT FOR           IF loopvar <= finish THEN EXIT FOR
         NEXT loopvar         NEXT loopvar
 +</code>
alternative_20for_20next_20behaviour.1522502345.txt.gz · Last modified: 2024/01/05 00:18 (external edit)