// Of course this is only an example, but except in rare cases when the value of a boolean is significant (e.g., interfacing code in different languages), don't compare to booleans! Not only is it redundant, it's another potential source of error.

if (!c_assert(p >= 0) == true) { return ERROR; }

// vs

if (!c_assert(p >= 0)) { return ERROR; }

// The following makes the error condition clearer, but it goes against the convention of having a hopefully true condition as the argument to assert.

if (c_assert(p < 0)) { return ERROR; }