Check out example codes for "get both item and index in c#". It will help you in understanding the concepts better.

Code Example 1

// add this to your namespace
public static IEnumerable<(T item, int index)> WithIndex<T>(this IEnumerable<T> source)
{
    return source.Select((item, index) => (item, index));
}

//do something like this

foreach (var (item, index) in collection.WithIndex())
{
    DoSomething(item, index);
}

Code Example 2

Array.IndexOf(arrName, searchingFor)

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