C# 0 The Complete Reference

PART I

C h a p t e r   1 9 :  

L I N Q  

557

PART IPART I

    double[] nums =  { -10.0, 16.4, 12.125, 100.85, -2.2, 25.25, -3.5 } ;

    // Create a query that returns the square roots of the

    // positive values in nums.

    var sqrRoots = from n in nums

                   where n > 0

                   select Math.Sqrt(n);

    Console.WriteLine("The square roots of the positive values" +

                      " rounded to two decimal places:");

    // Execute the query and display the results.

    foreach(double r in sqrRoots) Console.WriteLine("{0:#.##}", r);

  }

}

The output is shown here:

The square roots of the positive values rounded to two decimal places:

4.05

3.48

10.04

5.02

In the query, pay special attention to the 

select

 clause:

select Math.Sqrt(n);

It returns the square root of the range variable. It does this by obtaining the result of passing 

the range variable to 

Math.Sqrt( )

, which returns the square root of its argument. This means 

that the sequence obtained when the query is executed will contain the square roots of the 

positive values in 

nums

. If you generalize this concept, the power of 

select

 becomes apparent. 

You can use 

select

 to generate any type of sequence you need, based on the values obtained 

from the data source.

Here is a program that shows another way to use