字符串中的最后一个单词和第一个单词 c#

Question

i need to print the first and the last word in a string here is what i've tried

        Console.WriteLine("please enter a string");
        string str = Console.ReadLine();
        string first = str.Substring(0, str.IndexOf(" "));
        string last = str.Substring(str.LastIndexOf(' '),str.Length-1);
        Console.WriteLine(first + " " + last);

when i run the code this massage appear

Unhandled Exception: System.ArgumentOutOfRangeException: Index and length must refer to a location within the string. Parameter name: length at System.String.Substring(Int32 startIndex, Int32 length) at ConsoleApp1.Tar13.Main() in C:\Users\User\source\repos\ConsoleApp1\ConsoleApp1\Tar13.cs:line 16

i dont know what is the problem

Answer 1

If this is homework, don't hand this in unless you really understand it, have done LINQ (or have a supervisor that approves of off-piste learning and you're prepared to acknowledge you got outside assistance/did background learning) and are willing to explain it if asked:

    Console.WriteLine("please enter a string");
    string str = Console.ReadLine();
    string[] bits = str.Split();
    Console.WriteLine(bits.First() + " " + bits.Last());

For a non-LINQ version:

    Console.WriteLine("please enter a string");
    string str = Console.ReadLine();
    string first = str.Remove(str.IndexOf(' '));
    string last = str.Substring(str.LastIndexOf(' ') + 1);
    Console.WriteLine(first + " " + last);

Bear in mind that these will crash if there are no spaces in the string - the Split version won't

Look at String Remove and Substring

If you want to robust things up so it doesn't crash:

    Console.WriteLine("please enter a string");
    string str = Console.ReadLine();
    if(str.Contains(" ")){
      string first = str.Remove(str.IndexOf(' '));
      string last = str.Substring(str.LastIndexOf(' ') + 1);
      Console.WriteLine(first + " " + last);
    }

I'll leave a "what might we put in an else ?" in that last code block, as an exercise for you:)

Answer 2

you can split the string and get first and last...

   var s = str.Split(' ', StringSplitOptions.RemoveEmptyEntries );
   if(s.Length >= 2) 
   {
    var first = s.First();
    var last = s.Last();
    Console.WriteLine($"{first} {last}");
   }

Answer 3

In general case when sentence can contain punctuation , not necessary English letters you can try regular expressions . Let's define

Word is non empty sequence of letters and apostrophes

And so we have

Code:

  using System.Linq;
  using System.Text.RegularExpressions;

  ...

  private static (string first, string last) Solve(string value) {
    if (string.IsNullOrWhiteSpace(value))
      return ("", "");

    var words = Regex
      .Matches(value, @"[\p{L}']+")
      .Cast<Match>()
      .Select(m => m.Value)
      .ToArray();

    return words.Length > 0
      ? (words[0], words[words.Length - 1])
      : ("", ""); 
  }

Demo:

  string[] tests = new string[] {
    "Simple string",                 // Simple Smoke Test
    "Single",                        // Single word which is both first an last
    "",                              // No words at all; let's return empty strings
    "words, punctuations: the end.", // Punctuations
    "Русская (Russian) строка!",     // Punctuations, non-English words
  };

  var result = string.Join(Environment.NewLine, tests
    .Select(test => $"{test,-30} :: {Solve(test)}"));

  Console.Write(result);

Outcome:

Simple string                  :: (Simple, string)
Single                         :: (Single, Single)
                               :: (, )
words, punctuations: the end.  :: (words, end)
Русская (Russian) строка!      :: (Русская, строка)

Answer 4

If you want to get the last and first-word try to do the following:

string sentence = "Hello World"; //Sentence
string first = sentence.Split(" ")[0]; //First word
string last = sentence.Split(" ")[sentence.Split(" ").Length -1]; //Last word
Console.WriteLine(first + " "+ last);