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String.Concat Method (IEnumerable<String>)


Concatenates the members of a constructed IEnumerable<T> collection of type String.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

public static string Concat(
	IEnumerable<string> values


Type: System.Collections.Generic.IEnumerable<String>

A collection object that implements IEnumerable<T> and whose generic type argument is String.

Return Value

Type: System.String

The concatenated strings in values.

Exception Condition

values is null.

The method concatenates each object in values; it does not add any delimiters. To specify a delimiter between each member of values, call the Join(String, IEnumerable<String>) method.

An Empty string is used in place of any null argument.

Concat(IEnumerable<String>) is a convenience method that lets you concatenate each element in an IEnumerable(Of String) collection without first converting the elements to a string array. It is particularly useful with Language-Integrated Query (LINQ) query expressions. The following example passes a List(Of String) object that contains either the uppercase or lowercase letters of the alphabet to a lambda expression that selects letters that are equal to or greater than a particular letter (which, in the example, is "M"). The IEnumerable(Of String) collection that is returned by the Enumerable.Where<TSource> method is passed to the Concat(IEnumerable<String>) method to display the result as a single string.

using System;
using System.Collections.Generic;
using System.Linq;

public class Example
   public static void Main()
      string output = String.Concat( GetAlphabet(true).Where( letter => 
                      letter.CompareTo("M") >= 0));

   private static List<string> GetAlphabet(bool upper)
      List<string> alphabet = new List<string>();
      int charValue = upper ? 65 : 97;
      for (int ctr = 0; ctr <= 25; ctr++)
         alphabet.Add(Convert.ToChar(charValue + ctr).ToString());
      return alphabet; 
// The example displays the following output:

The following example uses the Sieve of Eratosthenes algorithm to calculate the prime numbers that are less than or equal to 100. It assigns the result to a List<T> object of type String, which it then passes to the Concat(IEnumerable<String>) method.

using System;
using System.Collections.Generic;

public class Example
   public static void Main()
      int maxPrime = 100;
      IEnumerable<String> primeList = GetPrimes(maxPrime);
      Console.WriteLine("Primes less than {0}:", maxPrime);
      Console.WriteLine("   {0}", String.Concat(primeList));

   private static IEnumerable<String> GetPrimes(int maxPrime)
      Array values = Array.CreateInstance(typeof(int), 
                              new int[] { maxPrime - 1}, new int[] { 2 }); 
      // Use Sieve of Erathsthenes to determine prime numbers.
      for (int ctr = values.GetLowerBound(0); ctr <= (int) Math.Ceiling(Math.Sqrt(values.GetUpperBound(0))); ctr++)

         if ((int) values.GetValue(ctr) == 1) continue;

         for (int multiplier = ctr; multiplier <=  maxPrime / 2; multiplier++)
            if (ctr * multiplier <= maxPrime)
               values.SetValue(1, ctr * multiplier);

      List<String> primes = new List<String>();
      for (int ctr = values.GetLowerBound(0); ctr <= values.GetUpperBound(0); ctr++)
         if ((int) values.GetValue(ctr) == 0) 
            primes.Add(ctr.ToString() + " ");
      return primes;
// The example displays the following output:
//    Primes less than 100:
//       2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

Universal Windows Platform
Available since 4.5
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Available since 4.0
Windows Phone Silverlight
Available since 7.1
Windows Phone
Available since 8.1
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