C++编程问题请大神赐教

为什么我输入Y或者N的时候会是这样？
现在正在下雨现在正在下雨吗
(Y/N)

#include
using namespace std;

int main()
{
char a;
int b;
while (a=1) {

    cout << "现在正在下雨吗" << '\n' << "(Y/N)" << endl;
    cin >> a;
    switch (a) {
    case 'Y':
        cout << "现在正在下雨";
        a = 2;
        break;
    case'N':
        cout << "现在没有下雨";
        a = 2;
        break;
    default:
        a = 1;





    }
}



return 0;

}

 // Q695122.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include <iostream>
using namespace std;

int main()
{
    char a = '1';
    int b;
    while (a=='1') {

        cout << "is raining now?" << '\n' << "(Y/N)" << endl;
        cin >> a;
        switch (a) {
        case 'Y':
            cout << "raining";
            a = '2';
            break;
        case'N':
            cout << "not raining";
            a = '2';
            break;
        default:
            a = '1';
        }
    }
    return 0;
}

while (a=1)
->
while (a==1)

while (a=1)
->
while (a=='1')

a = 2;
->
a = '2';

a = 1;
->
a = '1';

char a;
->
char a = '1';

while(a=1)会始终为真，应该是a==1吧