如何修复if语句的输出

Question

I'm making a program that reads in a date in the format MM DD YYYY and outputs what day of the week the date is. Here's the actual problem (I know it's long but it might help fix my problem):

Write a program that determines the day of the week for a given date. You can invent your own complex algorithm that takes into account the special leap year rules, and changes in calendars, but this is a case where it makes sense to look for things that are familiar. Who else might need to compute values from dates over a wide span of time? Historians work with dates, but generally don't compute from them. Astronomers, however, need to know the difference in time between orbital events in the solar system that span hundreds of years. Consulting an astronomy text, you will find that there is a standard way of representing a date, called the Julian Day Number (JDN). This value is the number of days that have elapsed since January 1, 4713 BC Given the JDN for a date, there is a simple formula that tells the day of the week:

DayOfWeek = (JDN + 1) % 7

The result is in the range of 0 to 6, with 0 representing Sunday.

The only remaining problem is how to compute the JDN, which is not so simple. The algorithm computes several intermediate results that are added together to give the JDN. We look at the computation of each of these three intermediate values in turn.

If the date comes from the Gregorian calendar (later than October 15, 1582), then compute intRes1 with the following formula; otherwise, let intRes1 be zero.

intRes1 = 2 – year / 100 + year / 400 (integer division)

The second intermediate result is computed as follows:

intRes2 = static_cast(365.25 * Year)

We compute the third intermediate value with this formula:

intRes3 = static_cast(30.6001 * (month + 1))

Finally, the JDN is computed this way:

JDN = intRes1 + intRes2 + intRes3 + day + 1720994.5

Your program should make appropriate use of value-returning functions in solving this problem. These formulas require nine significant digits; you may have to use the integer type long and the floating-point type double. Your program should prompt the user appropriately for input of the date; it should also properly label the output. Use proper coding style with comments to document the algorithm as needed.

Your program is to read from a file. The file consists of dates in the format: mm dd yyyy

I've tried changing the if (DayOfWeek = ) statements to if else statements with the final being else but it only outputs "Monday" no matter the date.

int main() {
    int JDN = 0;
    int DayOfWeek = 0;
    int res1 = 0;
    int res2 = 0;
    int res3 = 0;
    int day = 0;
    int month = 0;
    int year = 0;
    string final;
    ifstream inData;
    string file;
    cout << "Enter File Name: ";
    cin >> file;
    try {
        inData.open(file.c_str());
    }
    catch (int e) {
        return -1;
    }
    if (inData.is_open()) {
        inData >> month;
        inData >> day;
        inData >> year;
        if (month > 10 && day > 15 && year > 1582) {
            res1 = 2 - year / 100 + year / 400;
        }
        else {
            res1 = 0;
        }
        res2 = static_cast<int>(365.25 * year);
        res3 = static_cast<int>(30.6001 * (month + 1));
        JDN = res1 + res2 + res3 + day + 1720994.5;
        DayOfWeek = (JDN + 1) % 7;
        if (DayOfWeek = 0) {
            cout << "Sunday";
        }
        if (DayOfWeek = 1) {
            cout << "Monday";
        }
        if (DayOfWeek = 2) {
            cout << "Tuesday";
        }
        if (DayOfWeek = 3) {
            cout << "Wednesday";
        }
        if (DayOfWeek = 4) {
            cout << "Thursday";
        }
        if (DayOfWeek = 5) {
            cout << "Friday";
        }
        if (DayOfWeek = 6) {
            cout << "Saturday";
        }
    }
    else {
        cout << "File Not Found";
    }
    return 0;
}

The program outputs every day of the week on a single line when it should only output one. What is my problem?

Answer 1

Comparison is "=="; "=" is assignment.

You should have been getting compiler warnings, check the output more carefully.