【编程题目】求1+2+…+n, 要求不能使用乘除法、for、while、if、else、switch、case和条件语句

/*
题目： 计算 1+2+3+...+n
要求：不可用 乘除 if else for while switch case ?:
*/
#include <stdio.h>

const unsigned char b[16] = {1, 1<<1, 1<<2, 1<<3, 1<<4, 1<<5, 1<<6, 1<<7, 1<<8, 1<<9, 1<<10, 1<<11, 1<<12, 1<<13, 1<<14, 1<<15};

int get_add_factor(unsigned char n, unsigned char onebit)
{
     unsigned char b = onebit + (onebit<<1) + (onebit<<2) + (onebit<<3) + (onebit<<4) + (onebit<<5) + (onebit<<6) + (onebit<<7);
     return n&b;
}

int addn(unsigned char n)
{
    unsigned char bits[8] = {n&b[0], (n&b[1])>>1, (n&b[2])>>2 ,(n&b[3])>>3, (n&b[4])>>4, (n&b[5])>>5, (n&b[6])>>6, (n&b[7])>>7};  //把数字的每一位取出来
    int tmp[8] = {get_add_factor(n, bits[0]), get_add_factor(n, bits[1])<<1, get_add_factor(n, bits[2])<<2, get_add_factor(n, bits[3])<<3,
                  get_add_factor(n, bits[4])<<4, get_add_factor(n, bits[5])<<5, get_add_factor(n, bits[6])<<6, get_add_factor(n, bits[7])<<7};

    int pow = tmp[0] + tmp[1] + tmp[2] + tmp[3] + tmp[4] + tmp[5] + tmp[6] + tmp[7];
    int ans = (pow + n) >> 1;
    return ans;    
}

int main()
{
    //addn 的输入必须是 0 - 255
    int r = addn(255);

    return 0;
}

#include <stdio.h>  
#include <stdlib.h>  
#include <string.h>  
  
int add_fun(int n, int &sum)  
{  
    n && add_fun(n-1, sum);  //逻辑与 先计算左边的值 如果 左边的值不为真 则不会计算右边
    return (sum+=n);  
}  
  
int main()  
{  
    int sum=0;  
    int n=100;  
  
    printf("1+2+3+...+n=%d\n",add_fun(n, sum));  
  
    return 0;  
} 

#include <iostream>
using namespace std;

class Temp
{
public:
    Temp()
    {
        N++;
        SUM+=N;
    }
    static int GetSum()
    {
        return SUM;
    }
    static void Reset()
    {
        N = 0;
        SUM = 0;
    }
    ~Temp(){};
private:
    static int N;
    static int SUM;
}; //注意分号 别忘了

//初始化类的静态成员变量
int Temp::N = 0;
int Temp::SUM = 0;

int Sum(int n)
{
    Temp::Reset();
    Temp * a = new Temp[n];
    delete [] a;
    
    return Temp::GetSum();
}
int main()
{
    int a = Sum(100);
    return 0;
}

#include <iostream>  
using namespace std;  
  
typedef int (*fun)(int);  
  
int solution_f1(int i)  
{  
    return 0;  
}  

int solution_f2(int i)  
{  
    fun f[2]={solution_f1, solution_f2};  
    return i+f[!!i](i-1);  
}  
  
int main()  
{  
    cout<<solution_f2(100)<<endl;  
    return 0;
} 

#include <iostream>  
using namespace std;  
  
class A;  
A* Array[2];  
  
class A  
{  
public:  
    virtual int Sum(int n)  
    {  
        return 0;  
    }  
};  
  
class B:public A  
{  
public:  
    virtual int Sum(int n)  
    {  
        return Array[!!n]->Sum(n-1)+n;  
    }  
};  
  
int solution2_Sum(int n)  
{  
    A a;  
    B b;  
    Array[0]=&a;  
    Array[1]=&b;  
  
    int value=Array[1]->Sum(n);  
 
    return value;  
}  
  
int main()  
{  
    cout<<solution2_Sum(100)<<endl;  
    return 0;  
}