08-02. School club

This programme allows the student to enter their name, which is then saved on the end of a file.

At any time, the programme can be run again, a new student added to the file, and a list of all student names in the file can be output.

In our boilerplate, we need the I O library for file handling commands and the collections library, because we'll store the student names in a list when they're read from a file.

In the main programme, we'll call a subprogram called menu that will present the two options for the user.

Let's write that now.

Static void main in the menu subprogram, we'll output the two options to the screen.

That's sign up and show students.

We'll collect the choice the user makes in a variable called choice that we'll initialise to be an empty string.

We want to keep asking the user to enter a choice until they either choose number one or number two, so we need a while loop for that.

While Choice is not a 1 and choice is not 2.

Ask the user to enter their choice and collect the input.

Note that we don't use an if command to cheque if an input is valid, we should always use a while loop because we don't know how many invalid inputs the user will make before they enter the number 1 or 2.

Also note that 1 and 2 are actually strings and not numbers because they're inputs from the keyboard.

Inputs are always strings, and that's why 1 and 2 are in double quotes.

Okay, now we can do something based on the valid input switch choice.

In case the input was one, call the add student subprogram.

In case the input was two, call the show student subprogram.

And in each case we need to break out of the structure.

Once that's done, let's write the subprogram to add a student to the file.

Static void add student A pipe to a text file we'll identify as.

File is assigned to be an open file named programming.txt.

this time we want to add data to the end of the file without deleting what's already stored there.

So by putting true as an extra argument for the streamwriter, it will append or add to the end.

Instead of overwriting, Student is assigned the input.

Write that to a file with file writeline with the data in brackets.

Student, close the file and output a message to confirm to the user that the data is saved.

You have been signed up, followed by the student's name.

It's worth noting here that our file remained open while we waited for the user to input the name of the student.

This isn't the best idea because if the programme or computer crashes with the file open, it can cause file corruptions.

Ideally, we should collect the input first and then only open the file when we really need to.

Now we can write the subprogram to show all the students in the file.

Static void show students output a helpful message so the user understands what the data is.

List of strings identified as students is a new list of strings.

Stream reader file is assigned to be a new stream reader with the file called programming.txt.

in this programme, instead of reading all the data in one operation, we'll read it a line at a time.

This would allow you to do something with the data as you read it in.

For example, in this case we're going to add the students to a list.

So while the line we read in is not nothing or null, that is something has been read.

Add to the students list the line of data read from the file, trimming off the hidden end of line characters and then close the file.

This loop will mean the variable line holds a single line of data from the file in each iteration.

This is why the end of line markers were helpful when you type at the keyboard and press enter the computer adds that enter character to your file too.

But you can't see it unless you turn the visibility of formatting codes on in a file editor.

We can then use a for loop to output each student in the students list.

We could have output them as we were reading them from the file too.

Instead of reading them all in and then outputting them all, you might be thinking what's the point of the list?

Well, there isn't much point in this programme yet, but maybe we want to do something else with the data afterwards.

For example, sorting the names into alphabetical order.

Much easier to do if they are a list in memory.

That's the programme written showing you how to add to an existing file and and read data from a file a line at a time.