Problem in the for loop

Projects Programming
1

Hello,

This piece of code runs fine:

 for(int i = 7500; i < 12500; i+=5)
   {
     Serial.print("i = "); Serial.println(i);
     delay(500);
    }

if I change 7500 into 75000 and 12500 into 125000, the for-loop starts at 9464 and not at 75000. Anyone knows what is wrong?

Osiris

2

Welcome to the forum

Check carefully the range of values that an int can hold, particularly as it is a signed data type so can go negative

3

Review how big a number fits in an int.

Change your variable type to long.

a7

1 Like
4

Changing the int into a long fixed the problem.
Thank you very much!

Osiris

5

Did you understood the issue?

6

Yes I understand the issue (now). An Integer on arduino Uno is 16 bytes. MSB is the signed bit so that leaves : 15 bits(-1) = (2^15) - 1 = 32,767.
The number 75000 is to big for a 2 byte Integer and thus overflows twice:
75000 - 32,767 - 32,767 = 9466.

I also write software on a teensy 4.1 where an integer is 4 bytes. I forgot about the size of an integer on an arduino Uno.

Osiris

3 Likes
7

16 bits :wink:

1 Like
8

Thank you for correcting me. We have to stay correct. :slight_smile:

Osiris

9

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