bitwise operators - A clear, layman's explanation of the difference between | and || in c#?

Question

Ok, so I've read about this a number of times, but I'm yet to hear a clear, easy to understand (and memorable) way to learn the difference between:

if (x | y)

and

if (x || y)

..within the context of C#. Can anyone please help me learn this basic truth, and how C# specifically, treats them differently (because they seem to do the same thing). If the difference a given piece of code has between them is irrelevant, which should I default to as a best-practise?

Answer 1

|| is the logical-or operator. See here. It evaluates to true if at least one of the operands is true. You can only use it with boolean operands; it is an error to use it with integer operands.

// Example
var one = true || bar();   // result is true; bar() is never called
var two = true | bar();    // result is true; bar() is always called

| is the or operator. See here. If applied to boolean types, it evaluates to true if at least one of the operands is true. If applied to integer types, it evaluates to another number. This number has each of its bits set to 1 if at least one of the operands has a corresponding bit set.

// Example
var a = 0x10;
var b = 0x01;
var c = a | b;     // 0x11 == 17
var d = a || b;    // Compile error; can't apply || to integers
var e = 0x11 == c; // True

For boolean operands, a || b is identical to a | b, with the single exception that b is not evaluated if a is true. For this reason, || is said to be "short-circuiting".

If the difference a given piece of code has between them is irrelevant, which should I default to as a best-practise?

As noted, the difference isn't irrelevant, so this question is partially moot. As for a "best practice", there isn't one: you simply use whichever operator is the correct one to use. In general, people favor || over | for boolean operands since you can be sure it won't produce unnecessary side effects.