C# | Searching the index of specified object in Collection<T>

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: Output:

A
B
C
D
D
E
Index : 3

Example 2:

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://learn.microsoft.com/en-us/dotnet/api/system.collections.objectmodel.collection-1.indexof?view=netframework-4.7.2