How do I add text to a specific line in a text file in visual basic? - vb.net

Question

I am trying to create a program for an a level project using visual studio 2010 or 2017 at home, and am using a console application. What I need it to do is to create a text file with the students details which are entered to the program by the teacher. Then the teacher needs to be able to enter a specific student ID number and be able to add a score to the end of the record for this student.
This is my code so far and works as it should. But it only allows the teacher to enter the students details and writes it to the text file.
Dim studentID As String
Dim studentname As String
Dim classname As String
Dim Filename As String
Filename = “Students.txt”
FileOpen(1, Filename, OpenMode.Append)
Console.WriteLine(" Student Setup")
Console.WriteLine()
Console.WriteLine()
Console.Write("Student ID: ")
studentID = Console.ReadLine
Console.Write("Student Name: ")
studentname = Console.ReadLine
Console.WriteLine()
Console.Write("Class : ")
classname = Console.ReadLine
WriteLine(1, studentID, studentname, classname)
Console.WriteLine("Student successfully setup.")
Now I want to be able to allow the teacher to type in a students ID number and a score, and then write the score to the end of the specific line in the text file which begins with the students ID number.
An example of the text file will look like this:
"12345","Adam","A"
"67534","Alice","A"
"21456","Bob","A"
"98765","Charles","A"
"87654","Dennis","A"
Then if the teacher types in 21456 as the students ID number to add score to, and a score of 6 then it will add the number 6 to the end of this line, so that the line of the text file will now look like this:
"21456","Bob","A","6"
I have attempted to do this with the following code, which I got from another forum and tried to alter to do what I wanted to do:
Dim score As Integer
Dim studentIDenter As String
Dim count As Integer
Console.Write("Student ID to add score to: ")
studentIDenter = Console.ReadLine
Console.Write("Student score: ")
score = Console.readline
Dim lines() As String = System.IO.File.ReadAllLines(Filename)
For count = 0 To lines.Length - 1
If lines(count).StartsWith(studentIDenter) Then
lines(count) = studentID & studentname & classname & score
System.IO.File.WriteAllLines(Filename, lines)
End If
Next
FileClose(1)

Answer 1

I assume the user is NOT entering quotes around the student number and score.
You need to add the quotes in your check for a match at the beginning of the line. Additionally, you need to add a comma and quotes around the score when you add them to the end of the line.
Change to:
For count = 0 To lines.Length - 1
If lines(count).StartsWith(Chr(34) & studentIDenter & Chr(34)) Then
lines(count) = lines(count) & "," & Chr(34) & score & Chr(34)
System.IO.File.WriteAllLines(Filename, lines)
Exit For ' found the record, no need to keep looking
End If
Next

Answer 2

I have created the following:
Sub Main()
Dim studentID As String
Dim studentname As String
Dim classname As String
Dim addScoreSelection As String
Dim inputSID As String
Dim Filename As String
Filename = “Students.txt”
FileOpen(1, Filename, OpenMode.Append)
Console.WriteLine("Add a Score? Y/N")
addScoreSelection = Console.ReadLine.ToLower()
If addScoreSelection = "Y".ToLower() Then
FileClose(1)
Console.WriteLine("Enter a student ID: ")
inputSID = Console.ReadLine()
AddScore(inputSID)
ElseIf addScoreSelection = "N".ToLower() Then
Console.WriteLine("Student Setup")
Console.WriteLine()
Console.WriteLine()
Console.Write("Student ID: ")
studentID = Console.ReadLine
Console.Write("Student Name: ")
studentname = Console.ReadLine
Console.WriteLine()
Console.Write("Class : ")
classname = Console.ReadLine
WriteLine(1, studentID, studentname, classname)
Console.WriteLine("Student successfully setup.")
Else
Console.WriteLine("No selection made. Exiting.")
Process.GetCurrentProcess.Kill()
End If
End Sub
Sub AddScore(ByVal ID As String)
Dim Filename As String
Filename = “Students.txt”
Dim fileContent As String()
Dim index As Integer = 0
fileContent = IO.File.ReadAllLines(Filename)
For Each line As String In fileContent
If line.Contains(ID) Then
fileContent(index) = fileContent(index) & ",""6""" 'Pass in a ByVal param for this
Exit For
End If
index += 1
Next
IO.File.WriteAllLines(Filename, fileContent)
End Sub
I have added the sub routine AddScore that takes a student ID as a string param, I then use this parameter in a .Contains() to determine WHEN I have hit the line we are interested in in the text file.
I create a string array by reading all the text from the file
fileContent = IO.File.ReadAllLines(Filename)
I iterate through the array looking for the line in question, once the line is found I append the score to the end of the line (You will probably want to actually use a param here)
For Each line As String In fileContent
If line.Contains(ID) Then
fileContent(index) = fileContent(index) & ",""6""" 'Pass in a ByVal param for this
Exit For
End If
index += 1
Next
I then write the string array to the file
IO.File.WriteAllLines(Filename, fileContent)
This solves your issue I believe, but personally I am not happy with this. I don't like the idea of grabbing a whole lot of text and putting it into memory (imagine if we were reading a 5GB file...). The best solution in the long run would be to use the FileStream class to read/write it and find the line and append the text on said line.