| - bitwise OR

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#include <iostream>
#include <string>

int main(int argc, char **argv) {
    int a = 5;     // 0101b  (0x05)
    int b = 12;    // 1100b  (0x0C)
    int c = a | b; // 1101b  (0x0D)
    
    std::cout << "a = " << a << ", b = " << b << ", c = " << c << std::endl;
}

try online

a = 5, b = 12, c = 13

Why

A bit wise OR operates on the bit level and uses the following Boolean truth table:

true OR true = true
true OR false = true
false OR false = false

When the binary value for a (0101) and the binary value for b (1100) are OR’ed together we get the binary value of 1101:

int a = 0 1 0 1
int b = 1 1 0 0 |
        ---------
int c = 1 1 0 1

The bit wise OR does not change the value of the original values unless specifically assigned to using the bit wise assignment compound operator |=:

#include <iostream>
#include <string>

int main(int argc, char **argv) {
    int a = 5;  // 0101b  (0x05)
    a |= 12;    // a = 0101b | 1101b == 13

    std::cout << "a = " << a << std::endl;
}

try online

a = 13

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