Combine Monday to Sunday dates to textfile

Question

This is a C# 4.0 WinForms app.

I'm trying to pull all the Monday dates in a given month (the fully spelled out Month name and day), and the days in all the Sundays. Then, using StreamWriter, write these to a text file.

I found the following code suggestion on enumerating through a month, on StackOverFlow below.

How to get every monday of given month?

public static IEnumerable<DateTime> AllDatesInMonth(int year, int month)
{
    int days = DateTime.DaysInMonth(year, month);
    for (int day = 1; day <= days; day++)
    {
        yield return new DateTime(year, month, day);
    }
}

And then you can call with LINQ like so:

var mondays = AllDatesInMonth(2017, 7).Where(i => i.DayOfWeek == DayOfWeek.Monday);

I modified the suggestion to also pull the Sunday dates. I'm testing this, in order to make it part of a larger application.

This is what I've come up with so far, as shown below.

    private void btnTestDayOWeek_Click(object sender, EventArgs e)
    {
        int curYear = DateTime.Now.Year;
        int month = DateTime.Now.Month;

        string outputFile = @"C:\dates2Compare.txt";
        List<string> mondayList = new List<string>();
        List<string> sundayList = new List<string>();
        

        using (StreamWriter sw = new StreamWriter(outputFile))
        {
            var mondays = AllDatesInMonth(curYear, 3).Where(i => i.DayOfWeek == DayOfWeek.Monday);
            var sundays = AllDatesInMonth(curYear, 3).Where(i => i.DayOfWeek == DayOfWeek.Sunday);

            foreach (DateTime Monday in mondays)
            {
                mondayList.Add(Monday.ToString("MMMM d"));
            }
            
            foreach (DateTime Sunday in sundays)
            {
                sundayList.Add(Sunday.ToString("-d"));
            }
            
            var dayList = mondayList.Concat(sundayList);//attempt to join these 2-Lists

            foreach (string dt in dayList)
            {
                sw.WriteLine(dt);
            }
        }
    }

    public static IEnumerable<DateTime> AllDatesInMonth(int year, int month)
    {
        int days = DateTime.DaysInMonth(year, month);
        for (int day = 1; day <= days; day++)
        {
            yield return new DateTime(year, month, day);
        }
    }

I need to join the Monday to Sunday dates, like this, i.e.

March 1-7 
March 8-14

But this is what I'm receiving so far.

March 1
March 8
March 15
March 22
March 29
-7
-14
-21
-28

Can someone suggest how to modify my code so that, the text file that is written to, correctly displays the Monday date with a "-" after it and then the Sunday date?

score 1 · Accepted Answer · answered Mar 04 '21 at 21:29

You are making it too complicated. Simply loop the days of the month in a split second:

int year = 2021;
int month = 3;

DateTime date = new DateTime(year, month, 1);
string monthName = date.ToString("MMMM");
int ultimo = date.AddMonths(1).AddDays(-1).Day;

for (int i = 0; i < ultimo - 6; i++)
{
    DateTime monthDate = date.AddDays(i);
    if (monthDate.DayOfWeek == DayOfWeek.Monday)
    {
        string line = string.Format(monthName + " {0}-{1}", monthDate.Day, monthDate.Day + 6); 
        Console.WriteLine(line);
        // sw.WriteLine(line);
    }
}

Output:

March 1-7
March 8-14
March 15-21
March 22-28

this is exactly what I was looking for. I was using the posted solution I found earlier, but was unaware that I could simplify it as you've shown. — CodeMann, Mar 05 '21 at 19:59

score 0 · Answer 2 · answered Mar 04 '21 at 21:32

                //var dayList = mondayList.Concat(sundayList);//attempt to join these 2-Lists
                List<string> dayList = new List<string>();
                int weekCount = Math.Min(mondayList.Count(), sundayList.Count());
                for (int i = 0; i < weekCount; i++)
                {
                    string concateValue = mondayList[i] + sundayList[i];
                    dayList.Add(concateValue);
                }

When you Concat lists, the values stack on top of each other. You need to merge the lists together.

Combine Monday to Sunday dates to textfile

2 Answers2