C#
Date helpers
Add DateTime processing methods.
Date helpers
Our third helper is FormatDate: it turns a DateTime value into a consistent text form. Declaration: public static string FormatDate(DateTime date). In the body we use date.ToString("yyyy-MM-dd") to produce ISO format.
Example: Helpers.FormatDate(new DateTime(2024, 3, 15)) returns "2024-03-15". This format is sortable, human-readable, and machine-parseable. Keeping the date format in one place ensures consistency across the application.
DateTime formatting
The ToString method of DateTime takes a format string. yyyy gives a four-digit year, MM a two-digit month, dd a two-digit day. Case matters: MM is month, mm is minute.
The ISO 8601 standard yyyy-MM-dd is common in international commerce and databases. Local formats (e.g. dd.MM.yyyy) may be shown to users, but ISO is safe for storage and transfer.
Exercise Add the FormatDate method and call it
The Helpers class below already has Capitalize and Clamp. Now add a public static string FormatDate(DateTime date) method. In the body write return date.ToString("yyyy-MM-dd");. Inside Main print Helpers.FormatDate(new DateTime(2024, 3, 15)).
Show example solution
Add the FormatDate method to Helpers. In Main write Console.WriteLine(Helpers.FormatDate(new DateTime(2024, 3, 15)));
Example solution:
using System;
static class Helpers
{
public static string Capitalize(string text)
{
if (string.IsNullOrEmpty(text)) return text;
return char.ToUpper(text[0]) + text.Substring(1);
}
public static int Clamp(int value, int min, int max)
{
if (value < min) return min;
if (value > max) return max;
return value;
}
public static string FormatDate(DateTime date)
{
return date.ToString("yyyy-MM-dd");
}
}
class Program
{
static void Main()
{
Console.WriteLine("Ready");
Console.WriteLine(Helpers.Capitalize("hello"));
Console.WriteLine(Helpers.Clamp(15, 0, 10));
Console.WriteLine(Helpers.FormatDate(new DateTime(2024, 3, 15)));
}
}
Test yourself
-
Match each format to its output
- yyyy-MM-dd
- 2024-03-15
- dd/MM/yyyy
- 15/03/2024
- HH:mm
- 14:30
- yyyy
- 2024
-
Which is the ISO date format?
- dd/MM/yyyy
- MM-dd-yyyy
- yyyy-MM-dd
- yyyy:MM:dd
Show answer
yyyy-MM-dd — Correct. yyyy-MM-dd is the ISO 8601 standard.
-
Complete the FormatDate body
return date.ToString("____");
Show answer
return date.ToString("yyyy-MM-dd");
Next lesson: Putting it together
