Beginner-unfriendly behavior of long int initialization

[wagenadl]

Describe the request

Request: Implement IDE warnings for integer assignments that do not behave as a beginner would expect.

Rationale: Experienced C programmers will know that

long int x = 100 * 1000;

is a dangerous thing to write, because the two numbers will be interpreted as plain ints. As a consequence, when compiled on an Arduino Uno, the multiplication is interpreted as a 16-bit operation, and the end result will be x = 34,464. A beginner might reasonably expect that x = 100,000 at the end of this. While I fully realize that silent integer overflow is a problem with the C/C++ language rather than with the Arduino IDE per se, the fact is that may Arduino users may not be C/C++ experts. In fact, one of the key reasons that Arduino is so popular, is that for the most part you don't have to be a C/C++ expert to use it.

Another great example is

delay(66*1000)

which most people would expect to result in a 66 second delay. In fact, 66*1000 overflows to 464, so the actual delay is less than half a second.

If it is not possible to make the compiler understand the obvious intention in these cases, it would be really helpful if the IDE could flag this sort of thing with a visible warning.

Describe the current behavior

The Arduino IDE does not notice calculations where C quirks result in different results than a casual user would expect. No compiler warnings are generated either.

Arduino IDE version

2.0.1

Operating system

Linux

Operating system version

Ubuntu 22.04

Additional context

No response

Issue checklist

• I searched for previous requests in the issue tracker
• I verified the feature was still missing when using the latest nightly build
• My request contains all necessary details

[per1234]

Hi @wagenadl. Thanks for your suggestion.

No compiler warnings are generated either.

I'm happy to tell you that they are. You only need to enable warnings in your preferences and you'll get a nice warning like this:

C:\Users\per\AppData\Local\Temp\.arduinoIDE-unsaved2022103-716-a7vrx4.zaink\sketch_nov3a\sketch_nov3a.ino: In function 'void setup()':
C:\Users\per\AppData\Local\Temp\.arduinoIDE-unsaved2022103-716-a7vrx4.zaink\sketch_nov3a\sketch_nov3a.ino:3:18: warning: integer overflow in expression [-Woverflow]
 long int x = 100 * 1000;
              ~~~~^~~~~~

I'll provide instructions:

1. Select File > Preferences... from the Arduino IDE menus.
2. Select any value "Default" or higher from the "Compiler warnings" menu.
3. Click the OK button.

As for the idea of enabling compiler warnings by default in the IDE preferences, that is tracked here: #1630