stl的vector容器-n维向量的点积

C++的STL中的vector是一个动态数组，可以表示多维向量（一般平面二维向量对应的vector的size为2，三维对应的size为3), 求向量v的笛卡尔长度则为v点乘v自己的开平方根。

#include 
#include 
#include 

bool vetor_dot_mul(const std::vector& a, const std::vector& b, int n, double& res)
{
	if (a.size() != n || b.size() != n)
	{
		return false;
	}

	res = 0.0;
	for (int i = 0; i < n; i++)
	{
		double m = a[i] * b[i];
		res += m;
	}
}

double vector_length(const std::vector& a)
{
	double s = 0.0;
	vetor_dot_mul(a, a, a.size(), s);
	return sqrt(s);
}

int main()
{
	std::vector v0;
	v0.push_back(1.0); //[1.0]
	v0.push_back(1.2); //[1.0,1.2]
	v0.push_back(1.3); //[1.0,1.2,1.3]
	v0.push_back(1.4); //[1.0,1.2,1.3,1.4]

	std::vector v1 = {1.0,1.0,1.0,1.0};

	double v4dotmul = 0.0;
	vetor_dot_mul(v0, v1, 4, v4dotmul);
	
	std::cout << "R(4) vector dot mul: a*b = " << v4dotmul << std::endl;

	system("pause");

	return 0;
}