多种方法实现求和序列1+2+3+...+n

### 方法一：使用循环结构

#include 

int sumUsingLoop(int n)
{
    int total = 0;
    while (n > 0)
    {
        total += n;
        n--;
    }
    return total;
}

int main()
{
    printf("Sum: %d\n", sumUsingLoop(10));
    return 0;
}

### 方法二：利用递归函数

#include 

int sumUsingRecursion(int n)
{
    if (n == 1)
        return 1;
    else
        return n + sumUsingRecursion(n - 1);
}

int main()
{
    printf("Sum: %d\n", sumUsingRecursion(10));
    return 0;
}

### 方法三：基于类的构造函数

#include 
using namespace std;

class SumCalculator
{
public:
    SumCalculator() { currentNumber++; totalSum += currentNumber; }
    static int getTotalSum() { return totalSum; }
private:
    static int currentNumber;
    static int totalSum;
};

int SumCalculator::currentNumber = 0;
int SumCalculator::totalSum = 0;

int main()
{
    SumCalculator* calculators = new SumCalculator[10];
    cout <<"Sum: " <    delete[] calculators;
    return 0;
}

### 方法四：模板元编程（TMP）

#include 
using namespace std;

template<int N>
int sumUsingTemplate()
{
    return N + sumUsingTemplate1>();
}

template<>
int sumUsingTemplate<1>()
{
    return 1;
}

int main()
{
    cout <<"Sum: " <10>() <    return 0;
}