Sets (writes a 1 to) a bit of a numeric variable.
bitSet(x, n)
x: the numeric variable whose bit to set.
     n: which bit to set, starting at 0 for the least-significant (rightmost) bit.
x: the value of the numeric variable after the bit at position n is set.
Prints the output of bitSet(x,n) on two given integers. The binary representation of 4 is 0100, so when n=1, the second bit from the right is set to 1. After this we are left with 0110 in binary, so 6 is returned.
void setup() {
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }
  int x = 4;
  int n = 1;
  Serial.print(bitSet(x, n)); // print the output of bitSet(x,n)
}
void loop() {
}