1. Working with DateTime Data
ISYS 350

2. Declare DateTime Variable
Example: DateTime mydate;
Convert date entered in a textbox to DateTime data:
Use Convert:
mydate = Convert.ToDateTime(textBox1.Text);
Use DateTime class Parse method:
mydate = DateTime.Parse(textBox1.Text);
DateTime variable’s properties and methods:
MinValue, MaxValue
Year, month,DayOfWeek, hour, etc.
AddYear,AddDays,AddHours, etc.
Subtract
ToLongDateString, ToShortDateString

3. DateTime Example DateTime myDate;
myDate = DateTime.Parse(textBox1.Text);
MessageBox.Show(myDate.ToLongDateString());
MessageBox.Show(DateTime.MinValue.ToShortDateString());
MessageBox.Show(DateTime.MaxValue.ToShortDateString());

4. How to calculate the number of days between two dates?
TimeSpan class: TimeSpan represents a length of time. Define a TimeSpan variable:
TimeSpan ts;
We may use a TimeSpan class variable to represent the length between two dates:
ts = laterDate-earlierDate;

5. Code Example DateTime earlierDate, laterDate; double daysBetween;
TimeSpan ts;
earlierDate = DateTime.Parse(textBox1.Text);
laterDate = DateTime.Parse(textBox2.Text);
ts = laterDate-earlierDate;
daysBetween = ts.Days;
MessageBox.Show("There are " + daysBetween.ToString() + " days between " + earlierDate.ToShortDateString() + " and " + laterDate.ToShortDateString());
Note: Pay attention to how we create the output string.

6. Useful Properties and Method
Get current date:
DateTime thisDate=DateTime.Today;
Get current date and time:
DateTime thisDate=DateTime.Now;
Calculate # of days between two dates:
myDate = DateTime.Parse(textBox1.Text);
DaysBetween = thisDate.Subtract(myDate).Days;

7. Three Methods to Compute Age Given DOB: 1. Using Subtract method 2
Three Methods to Compute Age Given DOB: 1. Using Subtract method 2. Using Year property 3. Using TimeSpan Days
DateTime myDate, thisDate = DateTime.Today;
double Age;
myDate = DateTime.Parse(textBox1.Text);
Age = (thisDate.Subtract(myDate).Days / 365);
MessageBox.Show(Age.ToString());
Age = thisDate.Year - myDate.Year;
TimeSpan ts;
ts = thisDate - myDate;
Age = ts.Days / 365;

8. Compute Age Given DOB: Age<30, Young 30<=Age<65, Middle Age>=65, Old
DateTime myDate, thisDate=DateTime.Today;
double Age;
myDate = DateTime.Parse(textBox1.Text);
Age = (thisDate.Subtract(myDate).Days / 365);
MessageBox.Show(Age.ToString());
If (Age<30)
MessageBox.Show(“Young”);
elseif (Age<65)
MessageBox.Show(“Middle”);
else
MessageBox.Show(“Old”);

9. Date Comparison DateTime thisDate, currentDate = DateTime.Today;
thisDate = DateTime.Parse(textBox1.Text);
if (currentDate>thisDate)
MessageBox.Show("after");
else
MessageBox.Show("before");