求1+2+。。。+n

/*********************************************************************
题目:求1+2+3+....+n，要求不能使用乘除法，for、while、if、else、switch、
case等关键字及条件判断语句(A?B:C)。
*********************************************************************/
/*
*/
#include<stdio.h>
// ====================方法一====================
//利用构造函数
class Temp
{
public:
    Temp() { ++ N; Sum += N; }

    static void Reset() { N = 0; Sum = 0; }
    static unsigned int GetSum() { return Sum; }

private:
    static unsigned int N;
    static unsigned int Sum;
};

unsigned int Temp::N = 0;
unsigned int Temp::Sum = 0;

unsigned int Sum_Solution1(unsigned int n)
{
    Temp::Reset();

    Temp *a = new Temp[n];
    delete []a;
    a = NULL;

    return Temp::GetSum();
}

// ====================方法二====================
//利用虚函数
class A;
A* Array[2];

class A
{
public:
    virtual unsigned int Sum (unsigned int n) 
    { 
        return 0; 
    }
};

class B: public A
{
public:
    virtual unsigned int Sum (unsigned int n) 
    { 
        return Array[!!n]->Sum(n-1) + n; 
    }
};

int Sum_Solution2(int n)
{
    A a;
    B b;
    Array[0] = &a;
    Array[1] = &b;

    int value = Array[1]->Sum(n);

    return value;
}

// ====================方法三====================
//利用函数指针求解
typedef unsigned int (*fun)(unsigned int);

unsigned int Solution3_Teminator(unsigned int n) 
{
    return 0;
}

unsigned int Sum_Solution3(unsigned int n)
{
    static fun f[2] = {Solution3_Teminator, Sum_Solution3}; 
    return n + f[!!n](n - 1);
}

// ====================测试代码====================
void Test(int n, int expected)
{
    printf("Test for %d begins:\n", n);

    if(Sum_Solution1(n) == expected)
        printf("Solution1 passed.\n");
    else
        printf("Solution1 failed.\n");

    if(Sum_Solution2(n) == expected)
        printf("Solution2 passed.\n");
    else
        printf("Solution2 failed.\n");
}
void Test1()
{
    const unsigned int number = 1;
    int expected = 1;
    Test(number, expected);
}

void Test2()
{
    const unsigned int number = 5;
    int expected = 15;
    Test(number, expected);
}

void Test3()
{
    const unsigned int number = 10;
    int expected = 55;
    Test(number, expected);
}

void Test4()
{
    const unsigned int number = 0;
    int expected = 0;
    Test(number, expected);
}
int main()
{
    Test1();
    Test2();
    Test3();
    Test4();

    return 0;
}

求1+2+。。。+n,布布扣,bubuko.com

求1+2+。。。+n

原文：http://blog.csdn.net/walkerkalr/article/details/21551959