Introduction

1. Start Microsoft Visual C# and create a Console Application named WattsALoan1
2. To take advantage of the Visual Basic rich library, in the Solution Explorer, under WattsALoan1, right-click References and click Add Reference
3. In the Add Reference dialog box, click the .NET tab and click Microsoft.VisualBasic
    
   
4. Click OK
5. Change the Program.cs file as follows:
    

   using System; using System.IO; namespace WattsALoan1 { class Program { static int Main(string[] args) { string EmployerName, ApplicantName; string HomePhone, WorkPhone; double LoanAmount = 0.00D, InterestRate = 0.0D; double MonthlyPayment = 0.00D, Periods = 0D; Console.WriteLine(" -=- Car Loan Application -=-"); Console.WriteLine("Enter the following pieces " + "of information\n"); Console.WriteLine("Applicant Information"); Console.Write("Full Name: "); ApplicantName = Console.ReadLine(); Console.Write("Employer Name: "); EmployerName = Console.ReadLine(); Console.Write("Home Phone: "); HomePhone = Console.ReadLine(); Console.Write("Work Phone: "); WorkPhone = Console.ReadLine(); Console.WriteLine("Loan Estimation"); try { Console.Write("Amount of Loan: "); LoanAmount = double.Parse(Console.ReadLine()); } catch (FormatException) { Console.WriteLine("Invalid Loan Amount"); } try { Console.Write("Interest Rate(0 to 100): "); InterestRate = double.Parse(Console.ReadLine()) / 100; } catch (FormatException) { Console.WriteLine("Invalid Interest Rate"); } try { Console.Write("Number of Months: "); Periods = double.Parse(Console.ReadLine()); } catch (FormatException) { Console.WriteLine("Invalid Number of Months"); } try { MonthlyPayment = Microsoft.VisualBasic.Financial.Pmt(InterestRate / 12, Periods, -LoanAmount, 0, Microsoft.VisualBasic.DueDate.BegOfPeriod); } catch (ArgumentException) { Console.WriteLine("Some invalid values were provided\n"); } Console.WriteLine(); Console.WriteLine(" -=-=-=-=-=-=-=-=-=-=-=-=-=-="); Console.WriteLine(" -=- Car Loan Application -=-"); Console.WriteLine(" -=-=-=-=-=-=-=-=-=-=-=-=-=-="); Console.WriteLine("Applicant Information"); Console.WriteLine("Full Name: {0}", ApplicantName); Console.WriteLine("Employer Name: {0}", EmployerName); Console.WriteLine("Home Phone: {0}", HomePhone); Console.WriteLine("Work Phone: {0}", WorkPhone); Console.WriteLine("Loan Estimation"); Console.WriteLine("Loan Amount: {0:C}", LoanAmount); Console.WriteLine("Interest Rate: {0:P}", InterestRate); Console.WriteLine("Number of Months: {0:F}", Periods); Console.WriteLine("Monthly Payment: {0:C}\n", MonthlyPayment); return 0; } } }

6. Execute the application and test it. Here is an example:
    

   -=- Car Loan Application -=- Enter the following pieces of information Applicant Information Full Name: James Watts Employer Name: Wattson Enterprises Home Phone: (202) 374-4738 Work Phone: (301) 894-4789 Loan Estimation Amount of Loan: 12500 Interest Rate(0 to 100): 10.25 Number of Months: 48 -=-=-=-=-=-=-=-=-=-=-=-=-=-= -=- Car Loan Application -=- -=-=-=-=-=-=-=-=-=-=-=-=-=-= Applicant Information Full Name: James Watts Employer Name: Wattson Enterprises Home Phone: (202) 374-4738 Work Phone: (301) 894-4789 Loan Estimation Loan Amount: $12,500.00 Interest Rate: 10.25 % Number of Months: 48.00 Monthly Payment: $315.84 Press any key to continue...

7. Close the DOS window

The FileInfo class is equipped with one constructor whose syntax is:

public FileInfo(string fileName);

This constructor takes as argument the name of a file or its complete path. If you provide only the name of the file, the compiler would consider the same directory of its project. Here is an example:

FileInfo fleMembers = new FileInfo("First.txt");

Alternatively, if you want, you can provide any valid directory you have access to. In this case, you should provide the complete path.

The FileInfo constructor is mostly meant only to indicate that you want to use a file, whether it exists already or it would be created. Based on this, if you execute an application that has only a FileInfo object created using the constructor as done above, nothing would happen.

To create a file, you have various alternatives. If you want to create one without writing anything in it, which implies creating an empty file, you can call the FileInfo.Create() method. Its syntax is:

public FileStream Create();

This method simply creates an empty file. Here is an example of calling it:

FileInfo fleMembers = new FileInfo("First.txt");
fleMembers.Create();

The FileInfo.Create() method returns a FileStream object. You can use this returned value to write any type of value into the file, including text. If you want to create a file that contains text, an alternative is to call the FileInfo.CreateText() method. Its syntax is:

public StreamWriter CreateText();

This method directly returns a StreamWriter object. You can use this returned object to write text to the file.

When you call the FileInfo.Create() or the FileInfo.CreateText() method, if the file passed as argument, or as the file in the path of the argument, exists already, it would be deleted and a new one would be created with the same name. This can cause the right file to be deleted. Therefore, before creating a file, you may need to check whether it exists already. To do this, you can check the value of the Boolean FileInfo.Exists property. This property holds a true value if the file exists already and it holds a false value if the file doesn't exist or it doesn't exist in the path.

Here is an example of checking the existence of a file:

FileInfo fleMembers = new FileInfo("First.txt");
fleMembers.Create();

if( fleMembers.Exists == true )
	return;

As mentioned earlier, the FileInfo.Create() method returns a FileStream object. You can use this to specify the type of operation that would be allowed on the file.

To write normal text to a file, you can first call the FileInfo.CreateText() method. This method returns a StreamWriter object. The StreamWriter class is based on the TextWriter class that is equipped with Write() and WriteLine() methods used to write values to a file. The Write() method writes text on a line and keeps the caret on the same line. The WriteLine() method writes a line of text and moves the caret to the next line.

After writing to a file, you should close the StreamWriter object to free the resources it was using during its operation(s).

1. To allow the user to create a new employee, change the file as follows:
    

   using System; using System.IO; namespace WattsALoan1 { class Program { private static void CreateNewEmployee() { string employeeNumber, employeeName; FileInfo fleEmployees = new FileInfo("Employees.txt"); StreamWriter swrEmployees = fleEmployees.CreateText(); try { Console.WriteLine("Hiring New Employee"); Console.Write("Enter Employee Number as 00-000: "); employeeNumber = Console.ReadLine(); Console.Write("Enter Employee Name: "); employeeName = Console.ReadLine(); swrEmployees.WriteLine(employeeNumber); swrEmployees.WriteLine(employeeName); } finally { swrEmployees.Flush(); swrEmployees.Close(); } } static int Main(string[] args) { try { Console.Write("Do you want to hire a new " + "employee(0=No/1=Yes)? "); int answer = int.Parse(Console.ReadLine()); if (answer == 1) CreateNewEmployee(); } catch (FormatException) { Console.WriteLine("That was an invalid answer!\n"); } string EmployerName, ApplicantName; string HomePhone, WorkPhone; double LoanAmount = 0.00D, InterestRate = 0.0D; double MonthlyPayment = 0.00D, Periods = 0D; . . . No Change return 0; } } }

2. Execute the application. Here is an example:
    

   Do you want to hire a new employee(0=No/1=Yes)? 1 Hiring New Employee Enter Employee Number as 00-000: 44-228 Enter Employee Name: Johnny Olney

3. Close the DOS window

You may have created a text-based file and written to it. If you open such a file and find out that a piece of information is missing, you can add that information to the end of the file. To do this, you can call the FileInfo.AppenText() method. Its syntax is:

public StreamWriter AppendText();

When calling this method, you can retrieve the StreamWriter object that it returns, then use that object to add new information to the file.

1. To allow the user to add more employees to the file that holds their names, change the file as follows:
    

   using System; using System.IO; namespace WattsALoan1 { class Program { private static void CreateNewEmployee() { string employeeNumber, employeeName; FileInfo fleEmployees = new FileInfo("Employees.txt"); StreamWriter swrEmployees = null; // If the file exists already, then add the new employee to it if (fleEmployees.Exists == true) swrEmployees = fleEmployees.AppendText(); else // Otherwise, create a new file swrEmployees = fleEmployees.CreateText(); try { Console.WriteLine("Hiring New Employee"); Console.Write("Enter Employee Number as 00-000: "); employeeNumber = Console.ReadLine(); Console.Write("Enter Employee Name: "); employeeName = Console.ReadLine(); swrEmployees.WriteLine(employeeNumber); swrEmployees.WriteLine(employeeName); } finally { swrEmployees.Flush(); swrEmployees.Close(); } } static int Main(string[] args) { . . . No Change return 0; } } }

2. Execute the application
3. Type y to create an employee. Here is an example:
    

   Do you want to hire a new employee(0=No/1=Yes)? 1 Hiring New Employee Enter Employee Number as 00-000: 72-604 Enter Employee Name: Ernest Barzan

4. Close the DOS window