Q:

how can I specify file directory for csv file in c++? 

I'm not very good at c++ but I need to perform operations on data in csv file.  
the file is in the format of days versus classification such that for example, 
    revenues,profit,volume
    481.21,144.36,30
    449.13,134.74,28
    544.11,163.23,34
    368.93,110.68,23

so that first row specifies classification, and from 2nd row and forward, enlists day1, day2, day3 .... etc 
.cpp .csv and the executable program are in the same directory, but I suspected that it's not reading my file correctly. 
so I did a simple test and coded the following lines just to see if it can print the data as days versus classifications but it gives me 0's everywhere 
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
ifstream fin("data.csv");
int days = 1;
double revenues,profit,volume;
while (fin >> revenues >> profit >> volume){
    O[1][days] = revenues;
    O[2][days] = profit;
    O[3][days] = volume;
    days++;
}
for (int t = 1; t <= days; t++){
    for (int i = 1; i <= 3; i++){
        cout << O[i][t] << " ";
    }
    cout << endl;
}

A:

It's not important where the .cpp file is located.  It is important where the .exe file is located(compiled code which will be executed).  If both the .exe and the .csv file are in the same directory then it's all good. 
Your problem is the way you are reading; if you make a quick debug you will see that the while block is never executed because (fin >> revenues >> profit >> volume) will fail from the first time.  The reason is the way the extraction operator >> for streams work.  More details you can find everywhere (like here).  The short story: it fails to read a double from the stream because values are separated by commas.  It will read a string until a space shows (including the comma) and it will try to parse that string to a double and it will fail. 
You should try something like reading line by line.  You split the line into three values and use those. 
Or you can read strings until commas and parse those strings to double values.  I've put up some code:
string line;

while (fin.good()){
    std::getline (fin, line);
    stringstream line_stream(line);
    string value;

    std::getline (line_stream, value, ',');
    O[1][days] = atof(value.c_str());
    std::getline (line_stream, value, ',');
    O[2][days] = atof(value.c_str());
    std::getline (line_stream, value, ',');
    O[3][days] = atof(value.c_str());
    days++;
}

The std::getline() reads a string until newline or ','. 
Or you can simply search for some dedicated CSV library in C++ and use it directly. 