Use masks to select or set a particular flag bit : binary bit « Data Types « C++ Tutorial

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2. Data Types
3. binary bit

#include <iostream>
#include <iomanip>
using std::cout;
using std::endl;
using std::setfill;
using std::setw;

int main() {
  unsigned long flags = 0xFF;          // Flags variable
  unsigned long bit1mask = 0x1;        // Selects bit 1
  unsigned long bit6mask = 0x20;       // Selects bit 6
  unsigned long bit20mask = 0x80000;   // Selects bit 20
  
  cout << "\nSelect bit 1 from flags    : " << setw(8) << (flags & bit1mask);
  cout << "\nSelect bit 6 from flags    : " << setw(8) << (flags & bit6mask);
  cout << "\nSwitch off bit 6 in flags  : " << setw(8) << (flags &= ~bit6mask);

  cout << "\nSwitch on bit 20 in flags  : " << setw(8) << (flags |= bit20mask);

  cout << endl;

  return 0;
}

Select bit 1 from flags    :        1
Select bit 6 from flags    :       32
Switch off bit 6 in flags  :      223
Switch on bit 20 in flags  :   524511