An Interesting Pointer Puzzle

    int *a[] = { 1, 2, 3 }

Why? Because expressions of type int are being used to initialize elements of type pointer to int, without a cast.

The first step is operating your compiler such that you get the required diagnostics out of it, or at least the important ones, and then some. For instance, with gcc:

    # C90
    gcc -Wall -ansi ... # some would add -pedantic

    # C99
    gcc -Wall -std=c99 ...

And, of course, passing a pointer argument to a "%d" conversion specifier in printf is undefined behavior.