C++ 向量元素计数 [英] C++ Vector Elements Count

问题描述

在 C++ 中，使用向量头，我如何找到元素的数量?

In C++, using the vector header, how do I find the number of elements?

#include <iostream>
#include <cmath>
#include <fstream>
#include <cstdlib>
#include <vector>
using namespace std;
int primer(int max);
int main()
{
    system("pause");
    return 0;
    primer(1000);
}

int primer(int max){
    vector<int> a;
    a[1]=2;
    for (int i=2;i<=max;i++){
    bool prime=true;
    for (int ii=1;ii<=#a;ii++) {
    if i/a[ii]==math.floor(i/a[ii]) {
    prime=false;
    }
    }
    if prime==true {
    a[#a+1]=i;
    }
    }
    for (i=1;i<=#a;i++) {
    cout << a[i]);
    }
}
}

我最初写的代码对于 lua，这是我尝试将其转换为 C++.我会很感激细节，例如，一个坏线的特定替代品.我试图用 a.size 替换 #a，但没有用.

I originally wrote the code for lua, and this is my attempt to translate it to C++. I would appreciate specifics, for example, a specific replacement for a bad line. I tried to replace #a with a.size, but it didn't work.

修订:

#include <iostream>
#include <cmath>
#include <fstream>
#include <cstdlib>
#include <vector>
using namespace std;
int primer(int max);
int main()
{
    primer(5);
    system("pause");
    return 0;
}

int primer(int max){
    vector<int> a;
    a[1]=2;
    for (int i=2;i<=max;i++){
    bool prime=true;
    for (int ii=0;ii<a.size();ii++) {
    if (i/a[ii]==floor(i/a[ii])) {
    prime=false;
    }
    }
    if (prime==true) {
    a.push_back(i);
    }
    }
    for (int iii=0;iii<=a.size();iii++) {
    cout << a[iii] << endl;
    }
}

它没有运行就崩溃了.这是什么原因?

It crashes without running. For what reason is this?

推荐答案

a.size().

我建议使用某种参考资料，例如http://cplusplus.com/reference/stl/vector/.

I would recommend using some sort of reference material, e.g. http://cplusplus.com/reference/stl/vector/.

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