C# Capitalize first letter in in each sentence in a string

Question

I want to capitalize the first letter of each sentence in a string. I have a string, ex. "hello, how are you? i'm fine, you? i'm good. nice weather!"

and I want to capitalize the first letter of each sentence in it. So, "Hello, how are you? I'm fine, you?" etc.

EDIT: So far, I've just tried

public static string FirstCharToUpper(string input)
        {
            if (String.IsNullOrEmpty(input))
                throw new ArgumentException("ARGH!");
            return input.First().ToString().ToUpper() + input.Substring(1);
        }

but this capitalizes the first letter in each word, not sentence :/

Valentin · Accepted Answer · 2016-03-19T18:54:30.637

7

I suggest simple method, that iterates over the string.

You can also make it as an extension for a string.

public static class StringExtension
{
    public static string CapitalizeFirst(this string s)
    {
        bool IsNewSentense = true;
        var result = new StringBuilder(s.Length);
        for (int i = 0; i < s.Length; i++)
        {
            if (IsNewSentense && char.IsLetter(s[i]))
            {
                result.Append (char.ToUpper (s[i]));
                IsNewSentense = false;
            }
            else
                result.Append (s[i]);

            if (s[i] == '!' || s[i] == '?' || s[i] == '.')
            {
                IsNewSentense = true;
            }
        }

        return result.ToString();
    }
}

So, you can use it following way

 string str = "hello, how are you? i'm fine, you? i'm good. nice weather!".CapitalizeFirst();

So str equals to

Hello, how are you? I'm fine, you? I'm good. Nice weather!

edited Mar 19 '16 at 18:54

answered Mar 18 '16 at 16:47

Valentin

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@PaddiM8 It works for '?' '!' '.'. Look here `if (s[i] == '!' || s[i] == '?' || s[i] == '.')` – Valentin Mar 18 '16 at 16:54
Yea, I noticed. Really weird! – PaddiM8 Mar 18 '16 at 16:55
@PaddiM8 What is your sample? – Valentin Mar 18 '16 at 16:55
2

@PaddiM8 Add '\n' symbol also. – Valentin Mar 18 '16 at 16:56
@PaddiM8 I've updated last time, try it. You should add it to `s[i] != ' ' && s[i] != ',' && s[i] != '\n'` – Valentin Mar 18 '16 at 17:00
@PaddiM8 Probably, you need to add the '\t' symbol also. – Valentin Mar 18 '16 at 17:02
This was my exact solution but you beat me to it, might I suggest using `result += char.ToUpper(s[0]);` instead of converting a char to string. – maccettura Mar 18 '16 at 17:07
@PaddiM8 You can use `char.IsLetter(s[i])` instead of big if `s[i] != ' ' && s[i] != ',' && s[i] != '\n'` – Valentin Mar 18 '16 at 17:09
2

This is probably fine for common inputs, but the method should really be using a StringBuilder to increase perf/reduce memory pressure. – dlev Mar 19 '16 at 05:47
1

You know the length is going to be the same - initialize the `StringBuilder` capacity to be equal to `s.Length` by doing `new StringBuilder(s.Length)`. For even more performance, you could forego the `StringBuilder` entirely and use `char[]`. – Gediminas Masaitis Mar 19 '16 at 18:52

score 0 · Answer 2 · answered Mar 18 '16 at 16:35

Iterate over string: Create a list which holds stop characters.

Then check every letter in that string, if it is in the list or not. If it is in the list, then capitalize the character after that.

For first character, it's always uppercase, you should do it static.

Or, you can do it like Dan's said, it works too.

score 0 · Answer 3 · edited May 23 '17 at 11:48

Microsoft Outlook 2010 provides an option to format the selected text to a sentence case, please go to Format text Tab - Font group, you would find a change case option beside shrink font option, cutting long story short, you need something like that in your code to happen, unfortunately there is no built in property defined in .net.

However please have a look a the conversation already happened in stack overflow. .NET method to convert a string to sentence case

score 0 · Answer 4 · edited Mar 18 '16 at 17:11

0

You will need a text box called txtInput and another called txtOutput. Then run this code, e.g. upon a button press:

 bool Upper = true;
        foreach(char c in txtInput.Text)
        {
            if (Upper == true)
            {
                if (c == ' ')
                {
                    txtOutput.Text += c;
                    continue;
                }
                txtOutput.Text += c.ToString().ToUpper();
                Upper = false;
            }
            else
            {
                txtOutput.Text += c;
            }
            if (c == '?' || c == '!' || c == '.')
                Upper = true;


        }

Screen shot:

edited Mar 18 '16 at 17:11

Martin Zabel

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answered Mar 18 '16 at 16:55

César Caldeira

1

What about a symbols such as commas or tab symbol? – Valentin Mar 18 '16 at 17:02
Well... Won't work with new lines! @Valetin helped me though! Thank's anyways. – PaddiM8 Mar 18 '16 at 17:02

score 0 · Answer 5 · answered Sep 22 '22 at 17:02

It's been stated a few times, iterate over the character array. The primary reason for this is it keeps the string structure vs say a split, toupper/substring, and join.

Below handles a few scenarios, such as don't capitalize a letter after a digit. It also makes some assumptions in addition to those described/solved for above, hope it helps.

public static string CapitalizeFirstLetterInEachSentence(string sentences, bool capitalizeFirstSentence = true)
{
  bool capitalizeNextLetterOrDigit = capitalizeFirstSentence;
  char[] characters = sentences.ToCharArray();
  var len = characters.Length;

  for (int i = 0; i < len; i++)
  {
    var character = characters[i];
    switch (character)
    {
      case '.':
      case '?':
      case '!':
        capitalizeNextLetterOrDigit = true;
        continue;
    }
    
    if (capitalizeNextLetterOrDigit && char.IsLetterOrDigit(character))
    {
      capitalizeNextLetterOrDigit = false;
      characters[i] = char.ToUpper(character);
    }
  }
  return new string(characters);
}

C# Capitalize first letter in in each sentence in a string

5 Answers5