为什么无论输入如何，我的第一个 "if" 语句都会执行？

这就是正在讨论的程序，非常简短和甜蜜:

// Lab 5 Exercise 1
// Financial Aid Program
//
// Written by: Jared T. Fisher
#include <iostream>
#include <string>
using namespace std;
int main()
{
    long int _income; // declaring the variables
    char yesNo;
    cout << "Are you an undergrad student?"  ; // determining if they are an undergrad or not.
    cin >> yesNo;
    if ((yesNo = 'N') || (yesNo = 'n'))
    {
        cout << "You do not qualify for financial aid.";
    }
    else if ((yesNo = 'Y') || (yesNo = 'y'))
    {
        cout << "What is your current yearly income?";
        cin >> _income;
        if (_income <= 15000 && _income >= 0) // determining which aid they qualify for.
        {
            cout << "You qualify for $1000 of financial aid";
        }
        else if (_income > 15000)
        {
            cout << "You qualify for $500 of financial aid";
        }
        else
        {
            cout << "Your income must be greater than or equal to 0. Please close the program and try again.";
        }
    }
    else
    {
        cout << "Your inputted value must be either 'y' or 'n'. Please close   the program and try again.";
    }
    cout << endl << endl;
    return 0;
} // end function main()

总之，

1. 如果用户输入'n'或'n'，他们立即被告知他们不符合条件。

2. 如果用户输入"y"或"y"，则会询问他们的年收入，并由此计算出资格。

3. 如果用户输入了其他的输入，他们会得到一个错误消息。

然而，当我运行这个程序时，无论我输入'n'， 'y'还是'棉花糖'，它总是返回:

"You do not qualify for financial aid." 

好像我输入了'n'或'n'。我的代码有什么问题?