FOR...NEXT strange counting

[flotulopex]

Thank you keithdoxey,

It is not about to find a solution to make it work; it is about how the FOR...NEXT loop counts.

There are lots of differents solutions to solve my problem and I wonder how many people noticed this stange loop counting behaviour.

[keithdoxey]

It is not about to find a solution to make it work; it is about how the FOR...NEXT loop counts.

I think it is the same in any language.

you specify the start and end points for the count and optionally the step size.

the count starts at the specified start value then adds (or subtracts) the step value. It is then tested to see if it is within the range specified at which point the actions are executed. Once outside the specfied range it exits the for/next loop. This means that the value has to have changed from the last time the loop code was executed.

[Ioannis]

Hi Flotul

As I stated at #6 there is no strange behaviour. It is just the way for-next loops work in every version of Basic. Inside the loop the result is absolutely correct. Outside is expected to be +1 or -1 depending on the step of counting.

I see nothing strange here.
Other way to make a loop like While-Went or Repeat-Until use different counting methods.

While-wend for example, first checks, then executes. For-Next, first executes then checks.

Ioannis

[mister_e]

OK i'll try another explanation

    For Variable=0 to 255
        Pouet pouet
        next

The test is done at the FOR TO NEXT line, the incrementation is done at NEXT line.
So at the end the value=256... wich is really hard to fit in a BYTE variable. Hence it gives 0

Change your var to a WORD too see what's happen now.

    Repeat
        Pouet Pouet
        Variable = Variable +1
        Until Variable = 255

a Repeat Untill loop do the test at the end... so this why it worked

[flotulopex]

Thank you All,

All your explanations are absolutely clear.

[peterdeco1]

Hi Flotulopex. The FOR - NEXT is confusing to me too. I use a different routine from a basic compiler I used a long time ago. This is a snip from a motor speed controller that controls the speed of an electric cart. At the start of the program, LEFTRAMP is made 0. If the speedpot is reduced while running, it will also ramp down.

LEFTON: 'TURNS ON LEFT MOTOR FOR RIGHT TURN
ADCIN 2, SPEEDPOT
IF LEFTRAMP < SPEEDPOT Then LET LEFTRAMP = LEFTRAMP + 1
IF LEFTRAMP > SPEEDPOT Then LET LEFTRAMP = LEFTRAMP - 1
Pause 1 'CONTROLS THE RAMP-UP DELAY
HPwm 1,LEFTRAMP,15000 'PWM OUTPUT DUTYCYCLE LIMITED TO SPEEDPOT
GoTo LEFTON