小编XIA*_*ODI的帖子

string readString(string p)
{
    string s;

    cout << p;
    cin >> s;
    return s;
}

int main()
{
    string oper = readString("? ");
    while (oper != "Q")
    {
        if (oper == "l")
            cout << "load complete" << endl;
        else if (oper == "+")
            cout << "add complete" << endl;
        string oper = readString("? ");
    }
}

当我输入时l,输出是load complete.但后来我输入+,它仍然输出load complete.为什么不输出add complete？

http://ideone.com/JCDdXk

#include <string>
#include <iostream>
#include <vector>
#include <iomanip>

using namespace std;

class matrix
{
 public:
    matrix(int);
    void func(int);
    vector<vector<double> > m;
};

matrix::matrix(int size)
{
    //set 3 X 3 = 9 elements to zero
    vector<vector<int> > m(size, vector<int>(size));

    // success
    cout << "test1 if m[0][0] equals to zero: " << m[0][0] << endl;
}

void matrix::func(int size)
{
    // failure, can't pass till here
    cout << "test2 if m[0][0] equals to zero: " << m[0][0] << endl;

    for(int i = …