变量似乎在自行改变值

好的，所以我的项目是一个分析.txt文件的程序，该文件包含一堆不同长度的DNA链。我把它全部用于3个函数，但我的老师希望我们使用oo编程。所以我把我的代码放在一个类中，并把它分解成不同的函数。然而，现在我的变量似乎随机改变了它们的值，我不知道为什么。

我用我的"sum"变量运行了一系列测试（但它不是唯一一个这样做的变量），它计算出函数中的正确值，但如果我在main中重新计算"sum"的值，这个值就会变成一个荒谬的数字。

这是代码：问题变量在哪里以及如何使用它并不是我的整个程序。如果这还不足以显示问题，我可以添加更多，我只是不想让它变得混乱。

DNA处理.cpp

void DNAProcessing::CalcSumAndMean()
{
    int lineLength = 0;
    int lineCounter = 0;
    int wholeFileStringLen = 0;
    double sum = 0;
    double mean = 0;
    string wholeFileString = "";
    string line;
    bool filefail = false;

    ifstream DNAFile;
    DNAFile.open(nameoffile.c_str());

    if(DNAFile.fail())
    {
        filefail = true;
        return;
    }
    else
    {
        cout << "nYour data was processedn" << endl;
    }

    while(DNAFile >> line)
    {
        //cout << line << endl;
        lineCounter += 1;
        lineLength = line.length();
        sum += lineLength;

        wholeFileString += line;        
    }
    cout << "sum: " << sum << endl;  // with my test .txt file this outputs 736
    mean = (sum / lineCounter);
    wholeFileStringLen = wholeFileString.length();
    cout << "sum: " << sum << endl; // with my test .txt file this outputs 736
}

main.cpp

int main()
{
    srand(time(0));

    bool noexit = true;
    string yesorno;
    string filename;

    while(noexit == true)
    {
        cout << "Would you like to process a list of DNA strings? (y/n)" << endl;
        cin >> yesorno;

        if((yesorno == "y") || (yesorno == "Y" ))
        {
            cout << "please input the name of the file you wish to process." << endl;
            cin >> filename;

            DNAProcessing DNAStrandFile(filename);
            DNAStrandFile.CalcSumAndMean();
            cout << "sum: " << DNAStrandFile.sum << endl; //for some reason sum turns into 3.18337e-314 and i have no clue why
            if (DNAStrandFile.filefail == false)
            {
                cout << "sum: " << DNAStrandFile.sum << endl; // same here
                DNAStrandFile.CalcNucleobaseRelProb();
                DNAStrandFile.CalcBigramRelProb();
                DNAStrandFile.CalcVarianceAndStndDev();
                DNAStrandFile.CalcNormRand();
                DNAStrandFile.PrintData();
                DNAStrandFile.PrintNewList();
            }
            else
            {
                cerr << "No file found" << endl;
            }


        } 
        else if((yesorno == "n") || (yesorno == "N"))
        {
            noexit = false;
        } 
        else{}
    }
}

将我的test.txt文件传递到此程序时输出

sum: 736
sum: 736
sum: 3.18337e-314
sum: 3.18337e-314