位运算与函数指针

#include <stdio.h>
#include <string>
#include <algorithm>
using namespace std;

#define exchange(a,b) { a^=b; b^=a; a^=b; }
#define comp(a,b) ( (1ull<<((sizeof(a-b) * 8) - 1)) & (long long) floor((a-b)) ? b : a ) //不用任何大于小于符合比较两数大小
//函数指针
typedef int (*cmpFcn) (int);  //cmpFcn是一种指向函数指针类型的名字，该指针类型指向一个返回int类型，并带有一个int形参的函数

bool (*qt) (const string &, const string &);





int get(int a)
{
  a = a ^ ( a >> 1 );
  a = a ^ ( a >> 2 );
  a = a ^ ( a >> 4 );
  a = a ^ ( a >> 8 );
  a = a ^ ( a >> 16 );
  return a;
}

int getnum(int x)
{
  x = (x & 0x55555555) + ( (x>>1)&(0x55555555) );
  x = (x & 0x33333333) + ( (x>>2)&(0x33333333) );
  x = (x & 0x0F0F0F0F) + ( (x>>4)&(0x0F0F0F0F) );
  x = (x & 0x00FF00FF) + ( (x>>8)&(0x00FF00FF) ); 
  x = (x & 0x0000FFFF) + ( (x>>16)&(0x0000FFFF) );
  return x;

}

int main( )
{
  int a,b;
  while( scanf("%d%d",&a,&b) != EOF )
  {
    exchange(a,b);
    printf("交换后:");
    printf("%d %d\n",a,b); 
    printf("求a中有偶数个1还是奇数个1:\n");
    cmpFcn pf;
    pf = get;
    printf("16进制 a = %x\n",a);
    pf(a);
    if( !(a&1) ) puts("a中有偶数个1");
    else puts("a中有奇数个1");
    puts("求b中有多少个1");
    printf("16进制 b = %x\n",b);
    pf = getnum;
    printf("%d\n",pf(b));      

  }
  return 0;
}