c++ - 为什么第二个 'cin >>' 不会被处理？

Question

初学C++，去年学了Java，马上这个学期又要学C++密码学编程和MFC/API之类的东西，现在比较迷茫，总之请看代码:

#include <iostream>
#include <string>

using namespace std;

#define strSize 100

int main()
{
    char message[strSize];
    char cipher[strSize];
    char plaintext[strSize];
    int nCount;
    char nEKey, nDKey;

    for(int i=0; i<strSize; ++i)
    {
        message[i] = '\0';
        cipher[i] = '\0';
        plaintext[i] = '\0';
    }

    cout << "Please enter your confidential message:" << endl;
    cin.getline(message, strSize);
    nCount = cin.gcount();
    cout << nCount << " characters read." << endl;

    cout << "Enter secret key:" << endl;
    cin >> nEKey;
    for(int j=0; j<nCount-1; ++j)
        cipher[j] = message[j] + nEKey;
    cout << "Message is encrypted into:" << endl << cipher << endl << endl;

    cout << "Type your secret key again:" << endl;
    cin >> nDKey;

    for (int k=0; k<nCount-1; ++k)
        plaintext[k] = cipher[k] - nDKey;
    cout << "Cipher text is decrypted to:" << endl << plaintext << endl;

    return 0;
}

运行编译后的程序，结果为:

Please enter your confidential message:
hello world
12 characters read.
Enter secret key:
abc
Message is encrypted into:
袴?望答

Type your secret key again:
Cipher text is decrypted to:
gdkknvnqkc

我都用 g++ 和 visual studio 编译了它，它们产生了相同的输出。

现在我的问题是:为什么不处理第二个 cin？

在 visual studio 中它给了我一个警告说:

...\enc.cpp(25): warning C4244: '=' : conversion from 'std::streamsize' to 'int', possible loss of data

OMD，我是新手，不知道是什么意思，谁能帮忙修一下？

非常感谢!

Answer 1

nEKey 和nDKey 都是char类型，也就是说它们只能存储一个char。

cin >> nEKey 只读取abc 的a 后面的cin >> nDKey 读取b 是输入中的下一个字符。