The Sum() method in LINQ is used to calculate the sum of a sequence of values. It can be used with any sequence of numeric values, such as integers, floats, doubles, and decimals.

The syntax for the Sum() method is as follows:

C#

var sum = sequence.Sum(selector);

The sequence parameter is the sequence of values that you want to sum. The selector parameter is a function that takes a single element from the sequence and returns a numeric value.

For example, the following code uses the Sum() method to calculate the sum of all the numbers in an array:

C#

int[] numbers = { 1, 2, 3, 4, 5 };
var sum = numbers.Sum(x => x);

This code will first create an array of integers called numbers. Then, it will use the Sum() method to calculate the sum of all the numbers in the array. Finally, it will store the sum in a variable called sum.

The Sum() method can also be used with LINQ queries. For example, the following code uses the Sum() method to calculate the sum of all the prices in a table of products:

C#

var products = new LinqToSqlSumDataContext().Products;
var sum = products.Sum(x => x.Price);

This code will first create a LINQ query for the products table. Then, it will use the Sum() method to calculate the sum of all the prices in the table. Finally, it will store the sum in a variable called sum.