C++ 如何传递此特定代码的引用？

问：

请考虑以下几点：

void sum(vector<string> arr[], vector<string> columnName)
{
    int n, *sum = 0;
    cout << "Enter column number to calculate : ";
    cin >> n;
    cin.ignore(80, '\n');
    cout << columnName[n-1] << endl;
    for (auto item=arr[n-1].begin(); item!=arr[n-1].end(); item++)
    {
        if (item[0] == "1")
        {
            for (int i=1; i<sizeof(item[n-1]); i++)
            {
                // cout << item[i] << " ";
                sum += stoi(item[i]);  //how to reference this(the sum im talking about)
                 cout << sum << " ";
            }
            cout << sum << endl; // to become value of sum outside of the block here
        }
        else
            if (item[0] == "0")
            {
                cout << "Column can not be calculated" << endl;
                break;
            }
    }
    // return sum;
}

包含以下数据：

7
id,age,math,science,malay,chem,bio
0, 1, 1, 1, 1, 1, 1
5
1201101210,19,95,98,97,90,88
1201101490,12,87,100,92,100,70
1201101154,40,98,72,78,81,94
1201101376,23,40,50,70,79,100
1201101987,36,85,73,74,66,59

有一个带有局部变量的总和，我在注释中突出显示了它，我想将该总和从块中带到下面的块中（又名使局部变量全局）。我认为这可以通过使用引用传递来实现，但我不确定如何:(