How can you get the first digit in an int (C#)?

by

Benchmarks

Firstly, you must decide on what you mean by “best” solution, of course that takes into account the efficiency of the algorithm, its readability/maintainability, and the likelihood of bugs creeping up in the future. Careful unit tests can generally avoid those problems, however.

I ran each of these examples 10 million times, and the results value is the number of ElapsedTicks that have passed.

Without further ado, from slowest to quickest, the algorithms are:

Converting to a string, take first character

int firstDigit = (int)(Value.ToString()[0]) - 48;

Results:

12,552,893 ticks

Using a logarithm

int firstDigit = (int)(Value / Math.Pow(10, (int)Math.Floor(Math.Log10(Value))));

Results:

9,165,089 ticks

Looping

while (number >= 10)
    number /= 10;

Results:

6,001,570 ticks

Conditionals

int firstdigit;
if (Value < 10)
     firstdigit = Value;
else if (Value < 100)
     firstdigit = Value / 10;
else if (Value < 1000)
     firstdigit = Value / 100;
else if (Value < 10000)
     firstdigit = Value / 1000;
else if (Value < 100000)
     firstdigit = Value / 10000;
else if (Value < 1000000)
     firstdigit = Value / 100000;
else if (Value < 10000000)
     firstdigit = Value / 1000000;
else if (Value < 100000000)
     firstdigit = Value / 10000000;
else if (Value < 1000000000)
     firstdigit = Value / 100000000;
else
     firstdigit = Value / 1000000000;

Results:

1,421,659 ticks

Unrolled & optimized loop

if (i >= 100000000) i /= 100000000;
if (i >= 10000) i /= 10000;
if (i >= 100) i /= 100;
if (i >= 10) i /= 10;

Results:

1,399,788 ticks

Note:

each test calls Random.Next() to get the next int

More Related Contents:

  1. Filehandler in asp.net
  2. How do I find out what directory my console app is running in?
  3. Why does this (null || !TryParse) conditional result in “use of unassigned local variable”?
  4. Could not create SSL/TLS secure channel, despite setting ServerCertificateValidationCallback
  5. Declare and assign multiple string variables at the same time
  6. Sending and receiving UDP packets between two programs on the same computer
  7. ASP .NET Button event handlers do not fire on the first click, but on the second click after a PostBack
  8. How to get user information in DbContext using Net Core
  9. How to create Select List for Country and States/province in MVC
  10. Mouse Wheel Event (C#)
  11. Get all jobs in Quartz.NET 2.0
  12. C# Eval() support [duplicate]
  13. Is it possible to configure a Facebook app to be used across multiple domains?
  14. How to constrain generic type to must have a construtor that takes certain parameters?
  15. How to map fallback in ASP .NET Core Web API so that Blazor WASM app only intercepts requests that are not to the API
  16. Create a Deep Copy in C#
  17. Process.Start in C# The system cannot find the file specified error
  18. Selectively disabling UAC for specific programs on Windows Programatically
  19. Kinect SDK player detection
  20. How to detect if the mouse is inside the whole form and child controls?
  21. how to replace characters in a array quickly
  22. In the msdn guidance on Equals override, why the cast to object in the null check?
  23. What event catches a change of value in a combobox in a DataGridViewCell?
  24. Is there a way in Json.NET serialization to distinguish between “null because not present” and “null because null”?
  25. Garbage Collection not happening even when needed
  26. What is the “base class” for numeric value types?
  27. Why doesn’t C# use arithmetic overflow checking by default? [duplicate]
  28. Memory usage in C#
  29. Why does var evaluate to System.Object in “foreach (var row in table.Rows)”?
  30. How do I get a directory size (files in the directory) in C#?

Leave a Comment