To create a local variable in the LINQ statement, you can use the let operator. You must use it before the select statement to hold the result and you must initialize the variable. Normally, the variable can hold a constant value. At the end of the query, you can select that let variable and later use it as the returned value. Here is an example: using System;
using System.Linq;
using System.Drawing;
using System.Windows.Forms;
using System.Collections.Generic;
public class Exercise : Form
{
private Label lblPrincipal;
private TextBox txtPrincipal;
public Exercise()
{
InitializeComponent();
}
void InitializeComponent()
{
lblPrincipal = new Label();
lblPrincipal.Location = new System.Drawing.Point(12, 20);
lblPrincipal.AutoSize = true;
lblPrincipal.Text = "Principal:";
txtPrincipal = new TextBox();
txtPrincipal.Location = new System.Drawing.Point(80, 16);
txtPrincipal.Size = new System.Drawing.Size(80, 20);
txtPrincipal.TextAlign = HorizontalAlignment.Right;
Controls.Add(lblPrincipal);
Controls.Add(txtPrincipal);
Text = "Loan Evaluation";
Load += new EventHandler(ExerciseLoad);
Size = new System.Drawing.Size(204, 84);
}
private void ExerciseLoad(object sender, EventArgs e)
{
var loan = new double[] { 1250d, 12.05d, 36d };
var number = from n
in loan
let principal = 2465D
select principal;
foreach (var nbr in number)
{
txtPrincipal.Text = nbr.ToString();
}
}
[STAThread]
public static int Main()
{
System.Windows.Forms.Application.Run(new Exercise());
return 0;
}
}
This would produce:
If your query is based on an array, you can assign a value of that array to the let variable. You can get the value based on the index that represents its position in the array. Here is an example: private void ExerciseLoad(object sender, EventArgs e)
{
var loan = new double[] { 1250d, 12.05d, 36d };
var number = from n
in loan
let principal = loan[0]
select principal;
foreach (var nbr in number)
{
txtPrincipal.Text = nbr.ToString();
}
}
This would produce:
Instead of a constant value, you can create an expression and assign it to the let variable. The expression can be made of constant values. You can also use the members of the array by accessing each based on its index. Here is an example: using System;
using System.Linq;
using System.Drawing;
using System.Windows.Forms;
using System.Collections.Generic;
public class Exercise : Form
{
private Label lblAmountPaid;
private TextBox txtAmountPaid;
public Exercise()
{
InitializeComponent();
}
void InitializeComponent()
{
lblAmountPaid = new Label();
lblAmountPaid.Location = new System.Drawing.Point(12, 20);
lblAmountPaid.AutoSize = true;
lblAmountPaid.Text = "Amount Paid:";
txtAmountPaid = new TextBox();
txtAmountPaid.Location = new System.Drawing.Point(80, 16);
txtAmountPaid.Size = new System.Drawing.Size(80, 20);
txtAmountPaid.TextAlign = HorizontalAlignment.Right;
Controls.Add(lblAmountPaid);
Controls.Add(txtAmountPaid);
Text = "Loan Evaluation";
Load += new EventHandler(ExerciseLoad);
Size = new System.Drawing.Size(204, 84);
}
private void ExerciseLoad(object sender, EventArgs e)
{
var loan = new double[] { 800, 9, 4 }; // 1250d, 12.05d, 36d };
// Amount Paid = Principal(1 + Interest Rate * Periods)
// = Principal{1 + [(Interest Rate / 100) * (Periods in Months / 12)]}
var number = from n
in loan
let amtPaid = loan[0] * (1 + (loan[1] / 100 * loan[2]/12))
select amtPaid;
foreach (var nbr in number)
{
txtAmountPaid.Text = nbr.ToString();
}
}
[STAThread]
public static int Main()
{
System.Windows.Forms.Application.Run(new Exercise());
return 0;
}
}
This would produce:
You can declare more than one let variable. When you exit the statement, you can select only one of the variables and use it outside of the query. Here is an example: using System;
using System.Linq;
using System.Drawing;
using System.Windows.Forms;
using System.Collections.Generic;
public class Exercise : Form
{
private Label lblInterestPaid;
private TextBox txtInterestPaid;
public Exercise()
{
InitializeComponent();
}
void InitializeComponent()
{
lblInterestPaid = new Label();
lblInterestPaid.Location = new System.Drawing.Point(12, 20);
lblInterestPaid.AutoSize = true;
lblInterestPaid.Text = "Interest Paid:";
txtInterestPaid = new TextBox();
txtInterestPaid.Location = new System.Drawing.Point(90, 16);
txtInterestPaid.Size = new System.Drawing.Size(60, 20);
txtInterestPaid.TextAlign = HorizontalAlignment.Right;
Controls.Add(lblInterestPaid);
Controls.Add(txtInterestPaid);
Text = "Loan Evaluation";
Load += new EventHandler(ExerciseLoad);
Size = new System.Drawing.Size(180, 84);
}
private void ExerciseLoad(object sender, EventArgs e)
{
var loan = new double[] { 1250d, 12.05d, 36d };
// Future Value = Principal(1 + Interest Rate * Periods)
// = Principal{1 + [(Interest Rate / 100) * (Periods in Months / 12)]}
// Interest Paid = Future Value - Principal
var number = from n
in loan
let futurevalue = loan[0] * (1 + (loan[1] / 100 * loan[2] / 12))
let interestPaid = futurevalue - loan[0]
select interestPaid;
foreach (var nbr in number)
{
txtInterestPaid.Text = nbr.ToString("F");
}
}
[STAThread]
public static int Main()
{
System.Windows.Forms.Application.Run(new Exercise());
return 0;
}
}
This would produce:
You can include a where condition in your let variable if you want to check a condition. Here is an example: private void ExerciseLoad(object sender, EventArgs e)
{
var loan = new double[] { 1250d, 12.05d, 36d };
var number = from n
in loan
where loan[0] > 1000
let futurevalue = loan[0] * (1 + (loan[1] / 100 * loan[2] / 12))
select futurevalue;
foreach (var nbr in number)
{
txtFutureValue.Text = nbr.ToString("F");
}
}
The where statement can be included before or after the let statement and you would get the same result: private void ExerciseLoad(object sender, EventArgs e)
{
var loan = new double[] { 1250d, 12.05d, 36d };
var number = from n
in loan
let futurevalue = loan[0] * (1 + (loan[1] / 100 * loan[2] / 12))
where loan[0] > 1000
select futurevalue;
foreach (var nbr in number)
{
txtFutureValue.Text = nbr.ToString("F");
}
}
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