Warn for assignment in if() upon compilation

[robzach]

I often see students write if (x = y) when they mean if (x == y). An understandable error; even a prof of C++ taking one of my intro classes made this same mistake in his code and wasn't able to see it.

Apparently gcc can be made to warn of assignments in if tests, by using the -Wparentheses flag at compilation. The warning can be avoided by using an extra pair of parentheses to demonstrate programmer's intention, i.e. if ((x = y)).

GNU's gcc -Wparentheses documentation.

As many users of the Arduino IDE are newer programmers and unlikely to intend assignments this way, I recommend that the warning for assignments inside of if() tests be made visible in the console.

[PaulStoffregen]

Did you try this in File > Preferences?

[robzach]

Thanks, Paul!

I had overlooked that preference, and when I switched it to All, on compilation it threw exactly the right warning, helpfully painted orange to make it jump out: warning: suggest parentheses around assignment used as truth value [-Wparentheses].

I'll now suggest setting that preference as one of the initial IDE setup steps for my students.