C# | Searching the index of specified object in Collection<T> Last Updated : 01 Feb, 2019 Summarize Comments Improve Suggest changes Share Like Article Like Report Collection<T>.IndexOf(T) method is used to search for the specified object and returns the zero-based index of the first occurrence within the entire Collection<T>. Syntax: public int IndexOf (T item); Here, item is the object to locate in the List<T>. The value can be null for reference types. Return Value: This method returns the zero-based index of the first occurrence of item within the entire Collection<T>, if found, otherwise, -1. Below given are some examples to understand the implementation in a better way: Example 1: CSHARP // C# code to search for the specified // object and returns the zero-based // index of the first occurrence within // the entire Collection using System; using System.Collections.Generic; using System.Collections.ObjectModel; class GFG { // Driver code public static void Main() { // Creating a collection of strings Collection<string> myColl = new Collection<string>(); // Adding elements in Collection myColl myColl.Add("A"); myColl.Add("B"); myColl.Add("C"); myColl.Add("D"); myColl.Add("D"); myColl.Add("E"); // Displaying the elements in myColl foreach(string str in myColl) { Console.WriteLine(str); } // Searching for the specified object // and returns the zero-based index of // the first occurrence within the entire // Collection. If the object doesn't contain the // object, then -1 is returned Console.WriteLine("Index : " + myColl.IndexOf("D")); } } Output: A B C D D E Index : 3 Example 2: CSHARP // C# code to search for the specified // object and returns the zero-based // index of the first occurrence within // the entire Collection using System; using System.Collections.Generic; using System.Collections.ObjectModel; class GFG { // Driver code public static void Main() { // Creating a collection of ints Collection<int> myColl = new Collection<int>(); // Adding elements in Collection myColl myColl.Add(2); myColl.Add(3); myColl.Add(4); myColl.Add(5); // Displaying the elements in myColl foreach(int i in myColl) { Console.WriteLine(i); } // Searching for the specified object // and returns the zero-based index of // the first occurrence within the entire // Collection. If the object doesn't contain the // object, then -1 is returned Console.WriteLine("Index : " + myColl.IndexOf(7)); } } Output: 2 3 4 5 Index : -1 Note: The Collection<T> is searched forward starting at the first element and ending at the last element. This method determines equality using the default equality comparer EqualityComparer<T>.Default for T, the type of values in the list. This method performs a linear search. Therefore, this method is an O(n) operation, where n is Count. Reference: https://docs.microsoft.com/en-us/dotnet/api/system.collections.objectmodel.collection-1.indexof?view=netframework-4.7.2 Comment More infoAdvertise with us S Sahil_Bansall Follow Improve Article Tags : C# CSharp-method CSharp-Collections.ObjectModel-Namespace CSharp-Collection-Class Similar Reads C# Tutorial C# (pronounced "C-sharp") is a modern, versatile, object-oriented programming language developed by Microsoft in 2000 that runs on the .NET Framework. Whether you're creating Windows applications, diving into Unity game development, or working on enterprise solutions, C# is one of the top choices fo 4 min read Introduction to .NET Framework The .NET Framework is a software development framework developed by Microsoft that provides a runtime environment and a set of libraries and tools for building and running applications on Windows operating systems. The .NET framework is primarily used on Windows, while .NET Core (which evolved into 6 min read C# Interview Questions and Answers C# is the most popular general-purpose programming language and was developed by Microsoft in 2000, renowned for its robustness, flexibility, and extensive application range. It is simple and has an object-oriented programming concept that can be used for creating different types of applications.Her 15+ min read C# Dictionary Dictionary in C# is a generic collection that stores key-value pairs. The working of Dictionary is quite similar to the non-generic hashtable. The advantage of a Dictionary is, that it is a generic type. A dictionary is defined under System.Collections.Generic namespace. It is dynamic in nature mean 5 min read C# List Class In C#, the List<T> class represents the list of objects that can be accessed by index. It comes under the System.Collections.Generic namespace. List class can be used to create a collection of different types like integers, strings, etc. List<T> class also provides the methods to search, 7 min read C# Delegates A delegate is an object which refers to a method or you can say it is a reference type variable that can hold a reference to the methods. It provides a way which tells which method is to be called when an event is triggered. For example, if you click on a Button on a form (Windows Form application), 6 min read ASP.NET Interview Questions and Answer ASP.NET is a popular framework by Microsoft for building fast and scalable web applications. It allows developers to create dynamic websites, services, and apps, using server-side code and offering a user-friendly experience. Trusted by companies like Microsoft, Dell, and Accenture, ASP.NET is used 15+ min read C# .NET Framework (Basic Architecture and Component Stack) C# (C-Sharp) is a modern, object-oriented programming language developed by Microsoft in 2000. It is a part of the .NET ecosystem and is widely used for building desktop, web, mobile, cloud, and enterprise applications. This is originally tied to the .NET Framework, C# has evolved to be the primary 6 min read C# Data Types Data types specify the type of data that a valid C# variable can hold. C# is a strongly typed programming language because in C# each type of data (such as integer, character, float, and so forth) is predefined as part of the programming language and all constants or variables defined for a given pr 7 min read C# Arrays An array is a group of like-typed variables that are referred to by a common name. And each data item is called an element of the array. The data types of the elements may be any valid data type like char, int, float, etc. and the elements are stored in a contiguous location. Length of the array spe 8 min read Like