Explain First(), FirstOrDefault() function in LINQ with C#.

Question

Ashutosh Kumar Verma · Answer

First() vs FirstOrDefault() in LINQ (C#)
Both First() and FirstOrDefault() are used to retrieve the first element from a collection, but they behave differently when no matching element is found.
and 
First()
Returns the first element in the collection that matches a given condition.Throws an exception (InvalidOperationException) if no element is found.and 
Example-
find the first even number in the list,
and 
using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
   static void Main()
   {
       Listandlt;intandgt; numbers = new Listandlt;intandgt; { 3, 7, 8, 10, 15 };
       int firstEven = numbers.First(n =andgt; n % 2 == 0);
       Console.WriteLine("First Even Number: " + firstEven);
       // Output: First Even Number: 8
   }
}
Example (Throws Exception)
Listandlt;intandgt; numbers = new Listandlt;intandgt; { 1, 3, 5, 7 };
int firstEven = numbers.First(n =andgt; n % 2 == 0); // No even number exist.
// Throws: InvalidOperationException: "Sequence contains no matching element"
and 
FirstOrDefault()
Returns the first matching element, or the default value (null for reference types,
0 for numeric types) if no element is found.Does not throw an exception when no element matches.
Example-
and 
using System;
using System.Linq;
using System.Collections.Generic;
class Program
{
   static void Main()
   {
       Listandlt;intandgt; numbers = new Listandlt;intandgt; { 3, 7, 8, 10, 15 };
       int firstEven = numbers.FirstOrDefault(n =andgt; n % 2 == 0);
       Console.WriteLine("First Even Number: " + firstEven);
       // Output: First Even Number: 0 (if no even number exists)
       // Example with Strings
       Listandlt;stringandgt; names = new Listandlt;stringandgt; { "Alice", "Bob", "Charlie" };
       string result = names.FirstOrDefault(n =andgt; n.StartsWith("Z"));
       Console.WriteLine(result == null ? "No match found" : result);
       // Output: No match found
   }
}
and 
When to Use What?
When you are sure that at least one matching element exists, use First().When no matching element exists, use FirstOrDefault() (to avoid exceptions).
and 
Also, Read: 
LINQ Aggregate functions

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Explain First(), FirstOrDefault() function in LINQ with C#.

Amrith Chandran

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1 Answers

First() vs FirstOrDefault() in LINQ (C#)

First()

FirstOrDefault()

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