C# program to convert time from 12 hour to 24 hour format

Converting time from 12-hour format to 24-hour format in C# is a common requirement in applications. The DateTime.Parse() method can parse 12-hour time strings, and the ToString() method with the "HH:mm" format specifier converts it to 24-hour format.

Syntax

Following is the syntax for parsing 12-hour time and converting to 24-hour format −

DateTime dateTime = DateTime.Parse("12-hour time string");
string time24Hour = dateTime.ToString("HH:mm");

The HH format specifier represents hours in 24-hour format (00-23), while mm represents minutes (00-59).

Using DateTime.Parse() for Basic Conversion

The simplest approach uses DateTime.Parse() to convert a 12-hour time string to 24-hour format −

using System;

public class Program {
   public static void Main(string[] args) {
      DateTime d = DateTime.Parse("05:00 PM");
      Console.WriteLine("12-hour format: 05:00 PM");
      Console.WriteLine("24-hour format: " + d.ToString("HH:mm"));
      
      DateTime morning = DateTime.Parse("08:30 AM");
      Console.WriteLine("12-hour format: 08:30 AM");
      Console.WriteLine("24-hour format: " + morning.ToString("HH:mm"));
   }
}

The output of the above code is −

12-hour format: 05:00 PM
24-hour format: 17:00
12-hour format: 08:30 AM
24-hour format: 08:30

Using DateTime.ParseExact() for Specific Formats

For more control over the input format, use DateTime.ParseExact() −

using System;
using System.Globalization;

public class Program {
   public static void Main(string[] args) {
      string[] times12Hour = {"11:30 PM", "06:45 AM", "12:00 PM", "12:00 AM"};
      
      foreach(string time in times12Hour) {
         DateTime dt = DateTime.ParseExact(time, "hh:mm tt", CultureInfo.InvariantCulture);
         Console.WriteLine($"{time} ? {dt.ToString("HH:mm")}");
      }
   }
}

The output of the above code is −

11:30 PM ? 23:30
06:45 AM ? 06:45
12:00 PM ? 12:00
12:00 AM ? 00:00

Converting Multiple Time Formats

Here's a method that handles various 12-hour time formats and converts them to 24-hour format −

using System;

public class Program {
   public static string ConvertTo24Hour(string time12Hour) {
      try {
         DateTime dt = DateTime.Parse(time12Hour);
         return dt.ToString("HH:mm");
      }
      catch (FormatException) {
         return "Invalid time format";
      }
   }
   
   public static void Main(string[] args) {
      string[] testTimes = {
         "2:15 PM", "10:45 AM", "12:30 PM", 
         "12:30 AM", "9:00 PM", "1:05 AM"
      };
      
      Console.WriteLine("12-Hour ? 24-Hour Conversion");
      Console.WriteLine("?????????????????????????????");
      
      foreach(string time in testTimes) {
         Console.WriteLine($"{time,8} ? {ConvertTo24Hour(time)}");
      }
   }
}

The output of the above code is −

12-Hour ? 24-Hour Conversion
?????????????????????????????
 2:15 PM ? 14:15
10:45 AM ? 10:45
12:30 PM ? 12:30
12:30 AM ? 00:30
 9:00 PM ? 21:00
 1:05 AM ? 01:05

Key Points

• DateTime.Parse() automatically recognizes AM/PM indicators and converts accordingly.

• The "HH:mm" format specifier produces 24-hour time format.

• 12:00 PM converts to 12:00 (noon) and 12:00 AM converts to 00:00 (midnight).

• Always handle FormatException when parsing user input times.

Conclusion

Converting 12-hour to 24-hour format in C# is straightforward using DateTime.Parse() and the "HH:mm" format specifier. This approach handles AM/PM indicators automatically and provides accurate time conversion for various input formats.