Query Reuse

public void Linq101()
{
    // Deferred execution lets us define a query once
    // and then reuse it later after data changes.
  
    int[] numbers = new int[] { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
    var lowNumbers =
        from n in numbers
        where n <= 3
        select n;
  
    Console.WriteLine("First run numbers <= 3:");
    foreach (int n in lowNumbers)
    {
        Console.WriteLine(n);
    }
  
    for (int i = 0; i < 10; i++)
    {
        numbers[i] = -numbers[i];
    }
  
    // During this second run, the same query object,
    // lowNumbers, will be iterating over the new state
    // of numbers[], producing different results:
    Console.WriteLine("Second run numbers <= 3:");
    foreach (int n in lowNumbers)
    {
        Console.WriteLine(n);
    }
}

public void Linq101()
{
 
    // Deferred execution lets us define a query once
    // and then reuse it later in various ways.
    int[] numbers = new int[] { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };
    var lowNumbers = numbers.Where(num => num <= 3);
 
    Console.WriteLine("First run numbers <= 3:");
    foreach (int n in lowNumbers)
    {
        Console.WriteLine(n);
    }
 
    // Query the original query.
    var lowEvenNumbers = lowNumbers.Where(p => p % 2 == 0);
 
    Console.WriteLine("Run lowEvenNumbers query:");
    foreach (int n in lowEvenNumbers)
    {
        Console.WriteLine(n);
    }
 
 
    // Modify the source data.
    for (int i = 0; i < 10; i++)
    {
        numbers[i] = -numbers[i];
    }
 
    // During this second run, the same query object,
    // lowNumbers, will be iterating over the new state
    // of numbers[], producing different results:
    Console.WriteLine("Second run numbers <= 3:");
    foreach (int n in lowNumbers)
    {
        Console.WriteLine(n);
    }
}