Make first letter of a string upper case (with maximum performance)
The right way is to use Culture:
System.Globalization.CultureInfo.CurrentCulture.TextInfo.ToTitleCase(word.ToLower())
Note: This will capitalise each word within a string, e.g. "red house" --> "Red House". The solution will also lower-case capitalisation within words, e.g. "old McDonald" --> "Old Mcdonald".
public string FirstLetterToUpper(string str)
{
if (str == null)
return null;
if (str.Length > 1)
return char.ToUpper(str[0]) + str.Substring(1);
return str.ToUpper();
}
Old answer: This makes every first letter to upper case
public string ToTitleCase(string str)
{
return CultureInfo.CurrentCulture.TextInfo.ToTitleCase(str.ToLower());
}
Solution in different C# versions
C# 8 with at least .NET Core 3.0 or .NET Standard 2.1
public static class StringExtensions
{
public static string FirstCharToUpper(this string input) =>
input switch
{
null => throw new ArgumentNullException(nameof(input)),
"" => throw new ArgumentException($"{nameof(input)} cannot be empty", nameof(input)),
_ => string.Concat(input[0].ToString().ToUpper(), input.AsSpan(1))
};
}
Since .NET Core 3.0 / .NET Standard 2.1 String.Concat()
supports ReadonlySpan<char>
which saves one allocation if we use .AsSpan(1)
instead of .Substring(1)
.
C# 8
public static class StringExtensions
{
public static string FirstCharToUpper(this string input) =>
input switch
{
null => throw new ArgumentNullException(nameof(input)),
"" => throw new ArgumentException($"{nameof(input)} cannot be empty", nameof(input)),
_ => input[0].ToString().ToUpper() + input.Substring(1)
};
}
C# 7
public static class StringExtensions
{
public static string FirstCharToUpper(this string input)
{
switch (input)
{
case null: throw new ArgumentNullException(nameof(input));
case "": throw new ArgumentException($"{nameof(input)} cannot be empty", nameof(input));
default: return input[0].ToString().ToUpper() + input.Substring(1);
}
}
}
Really old answers
public static string FirstCharToUpper(string input)
{
if (String.IsNullOrEmpty(input))
throw new ArgumentException("ARGH!");
return input.First().ToString().ToUpper() + String.Join("", input.Skip(1));
}
This version is shorter. For a faster solution, take a look at Diego's answer.
public static string FirstCharToUpper(string input)
{
if (String.IsNullOrEmpty(input))
throw new ArgumentException("ARGH!");
return input.First().ToString().ToUpper() + input.Substring(1);
}
Probably the fastest solution is Darren's (There's even a benchmark) although I would change it's string.IsNullOrEmpty(s)
validation to throw an exception since the original requirement expects for a first letter to exist so it can be uppercased. Note that this code works for a generic string and not particularly on valid values from the Textbox
.