C ++不会添加传入的值

Question

When I pass in a value and assign it to another variable, it never seems to add them together. It only outputs both totals in the file, but not together. Can anyone point out my mistake?

void financialReport(int price)
{
    ofstream financial_log("financial.txt", ios::app);

    int total = 0;
    total += price;
    int test = total++;
    financial_log << "Total: " << test;


   financial_log.close(); 
}


    cout << "Destination:  ";
cin >> destination;
cout << "Price agreed: ";
cin >> price;

financialReport(price);

This is the output I get in my text file:

Total4Total5

Also, for some reason, there is no space between the total and the price.

Answer 1

It's a little hard to understand your question but I think one issue conuld be confusion about how the ++ operator works. variable_name++ will increment the variable after its evaluation in the current statement and ++variable_name will increment the variable before its evaluation in the current statement.

In your code above, ++ has no effect. If you want your variable test to have a value of one greater than total. Then you need to do this:

int test = ++total;

However, honestly in your case, that doesn't even make sense since total isn't used anywhere in the function after that. You would be better off just simply doing:

int test = total + 1;

Try opening a separate and specific questions about any ios or in/out formatting concerns.

It also looks like you're somehow trying to come up with a total across two function calls using a local variable which will never work because total will get reset to 0 on every function call.

I would be willing to bet that if you do as A. Yurchenko suggests you will probably find your own bug.

Answer 2

If you want to store total value in a file, you may use this:

void financialReport(int price) {

    ifstream financial_log_in("financial.txt");
    int total = 0;
    string dummy;
    while (financial_log_in >> dummy && dummy != "Total:") {
    }
    if (dummy == "Total:") {
        financial_log_in >> total;
    }

    ofstream financial_log_out("financial.txt");
    total += price;
    financial_log_out << "Total: " << total << endl;
    financial_log_out.close();
}

Here we read the current value from financial.txt , update it and write it back.

But in case you just call the function a few times during one runtime this will be more efficient:

void financialReport(int price) {
    static int total = 0;
    ofstream financial_log("financial.txt");
    total += price;
    financial_log << "Total: " total << endl;
}

This way financialReport(5); financialReport(6); financialReport(5); financialReport(6); will result in Total: 11 , but when you restart the program total will be 0 again.

Please, notice that both methods will overwrite financial.txt . If you don't want this behavior add ios::app flag to the constructor of the ofstream objects.