unsigned long型二进制数转十进制数

//c++模板元编程                                                  
#include <iostream>
using namespace std;

template<unsigned long N>
struct binary
{
    static unsigned const value = binary<N / 10>::value * 2 
        + N % 10;
};

template<>
struct binary<0>
{
    static unsigned const value = 0;
};

int main()
{
    cout << binary<1010>::value << endl;
    return 0;
}

 

//递归算法
#include <iostream>
using namespace std;

unsigned binary(unsigned long N)
{
    return 0 == N ? 0 : (N % 10 + 2 * binary(N / 10));
}
int main()
{
    cout << binary(1010) << endl;
    return 0;
}

 

//非递归算法

#include <iostream>
using namespace std;

unsigned binary(unsigned long N)
{
    unsigned result = 0;
    for(unsigned bit = 1; N; N /= 10, bit <<= 1) {
        if(N % 10) {
            result += bit;
        }
    }
    return result;
}
int main()
{
    cout << binary(1010) << endl;
    return 0;
}