Practical Learning: Introducing File Information
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- Start a new CLR Console
Application named WattsALoan2
- To take advantage of the Visual Basic rich library, in the Solution
Explorer, right-click WattsALoan2 and click References...
- In the Property Pages, click the Add New Reference button
- In the .NET tab, click
Microsoft.VisualBasic
- Click OK and click OK
- Change the source file file as follows:
// WattsALoan2.cpp : main project file.
#include "stdafx.h"
using namespace System;
int main(array<System::String ^> ^args)
{
String ^ EmployerName, ^ ApplicantName;
String ^ HomePhone, ^ WorkPhone;
double LoanAmount = 0.00, InterestRate = 0.0;
double MonthlyPayment = 0.00, Periods = 0;
Console::WriteLine(L" -=- Car Loan Application -=-");
Console::WriteLine(L"Enter the following pieces "
L"of information\n");
Console::WriteLine(L"Applicant Information");
Console::Write(L"Full Name: ");
ApplicantName = Console::ReadLine();
Console::Write(L"Employer Name: ");
EmployerName = Console::ReadLine();
Console::Write(L"Home Phone: ");
HomePhone = Console::ReadLine();
Console::Write(L"Work Phone: ");
WorkPhone = Console::ReadLine();
Console::WriteLine(L"Loan Estimation");
try {
Console::Write(L"Amount of Loan: ");
LoanAmount = double::Parse(Console::ReadLine());
}
catch(FormatException ^)
{
Console::WriteLine(L"Invalid Loan Amount");
}
try {
Console::Write(L"Interest Rate(0 to 100): ");
InterestRate = double::Parse(Console::ReadLine()) / 100;
}
catch(FormatException ^)
{
Console::WriteLine(L"Invalid Interest Rate");
}
try {
Console::Write(L"Number of Months: ");
Periods = double::Parse(Console::ReadLine());
}
catch(FormatException ^)
{
Console::WriteLine(L"Invalid Number of Months");
}
try {
MonthlyPayment =
Microsoft::VisualBasic::Financial::Pmt(InterestRate / 12,
Periods, -LoanAmount,
0, Microsoft::VisualBasic::DueDate::BegOfPeriod);
}
catch(ArgumentException ^)
{
Console::WriteLine(L"Some invalid values were provided\n");
}
Console::WriteLine();
Console::WriteLine(L" -=-=-=-=-=-=-=-=-=-=-=-=-=-=");
Console::WriteLine(L" -=- Car Loan Application -=-");
Console::WriteLine(L" -=-=-=-=-=-=-=-=-=-=-=-=-=-=");
Console::WriteLine(L"Applicant Information");
Console::WriteLine(L"Full Name: {0}", ApplicantName);
Console::WriteLine(L"Employer Name: {0}", EmployerName);
Console::WriteLine(L"Home Phone: {0}", HomePhone);
Console::WriteLine(L"Work Phone: {0}", WorkPhone);
Console::WriteLine(L"Loan Estimation");
Console::WriteLine(L"Loan Amount: {0:C}", LoanAmount);
Console::WriteLine(L"Interest Rate: {0:P}", InterestRate);
Console::WriteLine(L"Number of Months: {0:F}", Periods);
Console::WriteLine(L"Monthly Payment: {0:C}\n", MonthlyPayment);
return 0;
}
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- 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...
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- 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 = gcnew FileInfo(L"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 = gcnew FileInfo(L"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 = gcnew FileInfo(L"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 the Write()
and the 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).
Practical Learning: Writing to a File
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- To allow the user to create a new employee, change the file as
follows:
// WattsALoan2.cpp : main project file.
#include "stdafx.h"
using namespace System;
using namespace System::IO;
void CreateNewEmployee()
{
String ^ employeeNumber, ^ employeeName;
FileInfo ^ fleEmployees = gcnew FileInfo(L"Employees.txt");
StreamWriter ^ swrEmployees = fleEmployees->CreateText();
try {
Console::WriteLine(L"Hiring New Employee");
Console::Write(L"Enter Employee Number as 00-000: ");
employeeNumber = Console::ReadLine();
Console::Write(L"Enter Employee Name: ");
employeeName = Console::ReadLine();
swrEmployees->WriteLine(employeeNumber);
swrEmployees->WriteLine(employeeName);
}
finally
{
swrEmployees->Flush();
swrEmployees->Close();
}
}
int main(array<System::String ^> ^args)
{
try {
Console::Write(L"Do you want to hire a new "
L"employee(0=No/1=Yes)? ");
int answer = int::Parse(Console::ReadLine());
if( answer == 1 )
CreateNewEmployee();
}
catch(FormatException ^)
{
Console::WriteLine(L"That was an invalid answer!\n");
}
String ^ EmployerName, ^ ApplicantName;
String ^ HomePhone, ^ WorkPhone;
double LoanAmount = 0.00, InterestRate = 0.0;
double MonthlyPayment = 0.00, Periods = 0;
. . . No Change
return 0;
}
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- 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
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- 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.
Practical Learning: Appending to a File
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- To allow the user to add more employees to the file that holds their
names, change the file as follows:
// WattsALoan2.cpp : main project file.
#include "stdafx.h"
using namespace System;
using namespace System::IO;
void CreateNewEmployee()
{
String ^ employeeNumber, ^ employeeName;
FileInfo ^ fleEmployees = gcnew FileInfo(L"Employees.txt");
StreamWriter ^ swrEmployees = nullptr;
// 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 {
. . . No Change
}
finally
{
swrEmployees->Flush();
swrEmployees->Close();
}
}
int main(array<System::String ^> ^args)
{
. . . No Change
return 0;
}
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- Execute the application
- 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
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- Close the DOS window
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