// simulation using two classical bits
//
#include <stdio.h>

void X( int b[], int k) { b[k] = !b[k]; } // NOT on bit k

void CX( int b[], int c, int k) // controlled-NOT on bit k controlled by bit c, c != k
{
  b[k] ^= b[c]; // if( b[c]) b[k] = !b[k];
}

void print( const char msg[], int b[])
{
  printf( "%4s:", msg);
  for( int i = 1; i >= 0; --i) printf( " %i", b[i]);
  printf( "\n");
}

int main( void)
{
  int b[2] = { 0, 0 }; print( "b", b);
  X(b,1); print( "X", b);
  CX(b,1,0); print( "CX10", b);
}

/* output:

   b: 0 0
   X: 1 0
CX10: 1 1

*/