[c++] 헷갈리던 vector, 다시 공부

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• 이차원 벡터인 vector_2d에 vector1 과 vector2를 요소로 넣었다
• 이후 vector1 0번째 요소를 바꿨다
• vector1의 요소를 변경했으니 과연 vector_2d에도 변화가 있을까? 

#include <iostream>
#include <vector>
using namespace std;

int main()
{
	vector <int> vector1;
	vector <int> vector2;	
	vector1.push_back(10);
	vector1.push_back(20);	
	for (int i = 0; i < vector1.size(); i++)
	{
		cout << vector1.at(i) << endl;
	}
	cout << "===============" << endl;

	vector2.push_back(100);
	vector2.push_back(200);
	for (int i = 0; i < vector2.size(); i++)
	{
		cout << vector2.at(i) << endl;
	}
	cout << "===============" << endl;

	vector <vector<int>> vector_2d;
	vector_2d.push_back(vector1);
	vector_2d.push_back(vector2);

	cout << vector_2d.at(0).at(0) << endl;
	cout << vector_2d.at(0).at(1) << endl;
	cout << vector_2d.at(1).at(0) << endl;
	cout << vector_2d.at(1).at(1) << endl;
	cout << "===============" << endl;

	vector1.at(0) = 1000;

	cout << vector_2d.at(0).at(0) << endl;
	cout << vector_2d.at(0).at(1) << endl;
	cout << vector_2d.at(1).at(0) << endl;
	cout << vector_2d.at(1).at(1) << endl;
	cout << "===============" << endl;

	for (int i = 0; i < vector1.size(); i++)
	{
		cout << vector1.at(i) << endl;
	}

	return 0;
}

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출력하면 다음과 같다. 

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• 벡터와 배열을 사용한 평균 구하기

#include <iostream>
#include <vector>
using namespace std;

int main()
{
	vector<int> ary {13,20,30,40};
	int sum {0};

	for (int i = 0; i < ary.size(); i++)
	{
		sum = sum + ary.at(i);
	}
	cout << "sum : " << sum << endl;

	double avr {0.0};
	avr = static_cast<double>(sum) / ary.size();
	
	cout << "avr : " << avr << endl;;
	//==========================================
	int ary[]{ 13,20,30,40 };
	int ary_length = sizeof(ary) / sizeof(ary[0]);
	cout << ary_length << endl;

	int sum{};
	for (int i = 0; i < ary_length; i++)
	{
		sum += ary[i];
	}
	cout << "sum : " << sum << endl;

	double avr{ 0.0 };
	avr = static_cast<double>(sum) / ary_length;
	cout << "sum : " << sum << endl;

	return 0;
}