OR

OR places a 1 in the bitfield if either bitfields passed to it have a 1 in that position. If neither has a 1, it places a 0 in that position.

Truth Table:

Usage:

// A bitfield whose binary representation is: 00000000000000000000000000001010
integer a = 10;

// Another bitfield whose binary representation is: 00000000000000000000000000011001
integer b = 25;

// The next line translates to "store the result of OR'ing a and b together" in the variable a_OR_b.
// Its binary representation is 00000000000000000000000000011011, or 27.
integer a_OR_b = a | b;

 Here’s that operation written out longwise:

a      00000000000000000000000000001010 // As decimal = 10
b      00000000000000000000000000011001 // As decimal = 25
--------------------------------------------------------------------
a | b  00000000000000000000000000011011 // As decimal = 27

OR is useful in combining two bits, a good use of this would be executing some statements if the user has both the up arrow and down arrow pressed in the control event.

control(key controller, integer levels, integer edges) {
    // If user is pressing both the up arrow and down arrow:
    if ((levels & (CONTROL_FWD | CONTROL_BACK)) == (CONTROL_FWD | CONTROL_BACK)) {
        // The above statement translates to: "If levels has both the CONTROL_FWD and CONTROL_BACK bits set to 1"
    }
}

 Written out in longhand, the conditional statement looks like this:
The ORing operation, to get a bitfield with both CONTROL_FWD and CONTROL_BACK set to 1.

CONTROL_FWD                  00000000000000000000000000000001 // As decimal = 1
CONTROL_BACK                 00000000000000000000000000000010 // As decimal = 2
-----------------------------------------------------------------------------------------
(CONTROL_FWD | CONTROL_BACK) 00000000000000000000000000000011 // As decimal = 3

The ANDing operation, to see if the both CONTROL_FWD and CONTROL_BACK are set to 1 in levels.
In this case, levels is a bitfield in which CONTROL_FWD, CONTROL_BACK and CONTROL_UP are set to 1.

(CONTROL_FWD | CONTROL_BACK)          00000000000000000000000000000011 // As decimal = 3
levels                                00000000000000000000000000010011 // As decimal = 19
-----------------------------------------------------------------------------------------
levels & (CONTROL_FWD | CONTROL_BACK) 00000000000000000000000000000011 // As decimal = 3