Relational Operators

    These operate on integer or floating point values and return a 0 or 1 boolean value.

==		Equal
!=		Not Equal
>		Greater Than
<		Less Than
>=		Greater or Equal
<=		Less or Equal

    To see if x equals three, write something like:

    if (x == 3) …

    C does not have a distinct boolean type-- int is used instead. The language treats integer 0 as false and all non-zero values as true.

Pitfall = ≠ ==

    An absolutely classic pitfall is to write assignment (=) when you mean comparison (==). This would not be such a problem, except the incorrect assignment version compiles fine because the compiler assumes you mean to use the value returned by the assignment. This is rarely what you want

    if (x = 3) …

    This does not test if x is 3. This sets x to the value 3, and then returns the 3 to the if for testing. 3 is not 0, so it counts as “true” every time. This is probably the single most common error made by beginning C programmers. The problem is that the compiler is no help -- it thinks both forms are fine, so the only defense is extreme vigilance when coding. Or write “= ≠ ==” in big letters on the back of your hand before coding. This mistake is an absolute classic and it’s a bear to debug. Watch Out! And need I say: “Professional Programmer’s Language.”