Can I use tryParse output parameters to populate an array in a for-loop?

Question

I've got a homework stickler for which I need another set of eyes. The assignment is to create a program that prompts for a Student's name, then iterates through an array of days (String[] days = {"Sunday","Monday","Tuesday","Wednesday","Thursday","Friday","Saturday"};) prompting for a number of hours studied each day. Finally, the program is to display the daily average number of hours studied for the week.

I'm stuck with the data entry method:

    public void EnterHours()
    {
         // entry area header
        Console.WriteLine("Enter study hours for {0} ", name);
        for (int i = 0; i < days.Length; i++) 
        {
            Console.Write("{0}'s study hours: ", days[i]);
            string dailyHours = Console.ReadLine();
            int.TryParse(dailyHours, out hours[i]);    // problematic statement
        }
        SumHours(hours);
    }

Currently, the name variable is a property that's already been set; days is the String[] above, and I've instantiated hours as int[] hours; with the same scope as days. SumHours is another method that accepts int[] hours as a parameter and iterates through the array summing the values.

When I run the program, the console displays

Enter study hours for John Doe

Sunday's study hours:

but no matter what I enter, I end up with a Null Reference Exception. I'm also getting the following warning message:

Warning 1   Field 'Midterm.StudentHour.hours' is never assigned to, and will always have its default value null C:\Users\Dan\Dropbox\_MATC\ITDEV115\Assignments\Midterm\StudentHour.cs  11  15  Midterm

I've tried instantiating hours as int[] hours = new int[7]; but get the same error, so I suspect it's something with the way I'm outputting the parsed integer, but I'm not sure what to look at beyond that to solve the problem. Ideas? Hints?

There's no point to use TryParse without checking its result. You will not know if the parsing didn't succeed. — Display Name
– Display Name, Commented Oct 6, 2013 at 16:20
Can you provide me more detail like the code you used to initialize StudentHour class, StudentHour class constructor? — Doan Cuong
– Doan Cuong, Commented Oct 6, 2013 at 16:21
Problem with assignment to array cell can be solved by introducing temporary variable. — Display Name
– Display Name, Commented Oct 6, 2013 at 16:21
If you declare the int array as int[] hours you will get the null reference exception at the TryParse. If you declare as int[] hours = new int[7] then it should work. Do you have a different exception then? — Steve
– Steve, Commented Oct 6, 2013 at 16:24
It seems like a Dictionary would serve good purpose in this application. — Rohan
– Rohan, Commented Oct 6, 2013 at 16:30

terrybozzio · Accepted Answer · 2013-10-06 16:59:53Z

0

I think this will help you out:

        String[] days = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };
        Dictionary<string, int> hours = new Dictionary<string, int>();
        for (int i = 0; i < days.Length; i++)
        {
            int dailyHours;
            Console.Write("{0}'s study hours: ", days[i]);
            while (int.TryParse(Console.ReadLine(), out dailyHours) != true)
            {
                Console.WriteLine("Wrong input,must be only numbers!!!");
                Console.Write("{0}'s study hours: ", days[i]);
            }
            //if(int.TryParse(Console.ReadLine(),out dailyHours))
            hours.Add(days[i], dailyHours);
        }

Instead of string array you could use an enum with those values.

edited Oct 6, 2013 at 16:59

answered Oct 6, 2013 at 16:40

terrybozzio

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Comments

JLe · Accepted Answer · 2013-10-06 16:25:31Z

There must be some error with your declaration, since int[] hours = new int[7] shouldn't give you the null reference exception. Use the return of TryParse as well to check whether the input was valid. The following code works for me:

string[] days = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };
string name = "JLe";
int[] hours = new int[7];

Console.WriteLine("Enter study hours for {0} ", name);
for (int i = 0; i < days.Length; i++) {
    Console.Write("{0}'s study hours: ", days[i]);
    string dailyHours = Console.ReadLine();

    while (!int.TryParse(dailyHours, out hours[i])) {
        Console.Write("Please try again: ");
        dailyHours = Console.ReadLine();
    }
}
SumHours(hours);

Nikhil Agrawal · Accepted Answer · 2013-10-06 16:26:35Z

0

Your code is running fine. Here is the proof.

enter image description here

answered Oct 6, 2013 at 16:26

Nikhil Agrawal

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Comments

Itzik Gili · Accepted Answer · 2013-10-06 16:28:23Z

0

You did not initialize the array "hours" before assigning a value into it.

answered Oct 6, 2013 at 16:28

Itzik Gili

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Don 1234 · Accepted Answer · 2025-03-08 04:51:37Z

0

string[] days = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" };
string name = "JLe";
int[] hours = new int[7];

Console.WriteLine("Enter study hours for {0} ", name);
for (int i = 0; i < days.Length; i++) {
    Console.Write("{0}'s study hours: ", days[i]);
    string dailyHours = Console.ReadLine();

    while (!int.TryParse(dailyHours, out hours[i])) {
        Console.Write("Please try again: ");
        dailyHours = Console.ReadLine();
    }
}
SumHours(hours);

answered Mar 8 at 4:51

Don 1234

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Community Mar 8 at 15:13

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