Hey guys welcome to another visual basic tutorial by the Magic Monk. This tutorial
is actually requested by one of the YouTube users who needs some help with an
assignment so here it is the first thing i want to talk about is how to open up a
text file and load up the text file and print the contents in your program now
the reason why you want to be able to do that is because later on we're going to
teach you guys how to save data into a text file but that's a bit more
complicated so the first thing we're going to do is learn how to open up the
file first okay so the first thing I want you guys to do is click on new
project so I've just opened up Visual Basic 2010 Express and so right now this
is just a welcome screen and I want you guys to click on new projects and I just
want a windows form application and the name of it I'm going to call it text
file tutorial 1 text file tutorial 1 so I'm going to click OK and you can see
that the project has been created now what I want you to do is click save save all
and then where it says save project I want you to remember the location of the
project and the name of the project and click Save ok so now that we have saved
the project I'll make sure you really do click Save or otherwise
it's not going to work what we're going to do now is simply in this project
create a button and a label now what's going to happen is when I click this
button we're going to load up a text file and the contents of that text
file is going to be displayed in this label okay so I'm going to call
this button read from file so click on that and change the text to read from
file so now you can see the button as the words have just changed and now
we're going to double click on the button and we're going to enter in some
code for the button and the first line of code I'm going to type in dim
space file num as integer equals three file brackets now what this does is the
free file function what it does is it returns an integer our value that
represents the next file number available so basically every file that
you open up is going to have a file number and people who get mixed up with
which file number represents which file they'll probably lose track of what file
numbers they have used so free file is simply a function that returns a number
where there's a spare integer value for your file to be assigned for you to your
file so
anyway that integer is going to be stored in the variable file num and I'm
going to create declare another variable called string sorry
temp s as string and we're going to explain what that does in a second but
basically right now all you need to understand is it's a string variable
called temp s and I'm also going to declare another another string variable
called tempL okay so we have three variables the first string variable has
a value of nothing and the second string variable has not been
assigned any values okay now we're going to run the function file open and this
is the function that opens the text file now the first argument that it wants is
the file number now notice how we have already stored the file number into a
variable called file num so that's the first thing we typed in and then the next
thing it wants is the file name as a string now I'm just going to put in
"test.txt and we're going to create that file very
soon actually let's call it score.txt and we're going to create that file in a
second and then you're going to type in openmode. and you can see there's
five options here and basically you need to decide
what you're opening your file up for if you're opening it to write to it or to
read from it or to append to it now right now we just want to read from it
so it's OpenMode.Input and you can think of this as inputting the contents
of that file into our program so that's why it's called input ok and now we want
to use a do until loop now the difference between do until and
do-while is that do until will repeat a set of instructions until this condition
here is true so basically right now this condition is false so it will keep
repeating everything that I'm putting in this section now what does this part say
this part is saying that until the end of the file has been reached right so
this is file number whatever number it is we've opened it up and we're going to
keep working on whatever it is that we tell it to do until we reach the end of
the file so what are we going to do well that's going to require us to use the
temp l variable which we created earlier and what we're going to do is we're
going to get one line at a time so this is going to get the first line so line
input basically it reads a single line from the file so it's going to read that
first line from this file number which is school.txt so it's going to read that
that first line and put the contents into the variable tempL
and then what we're going to do is we're going to add this whole line into
our string variable tempS so tempS is going to equal sorry I'm going to use
the increment operator so I'm adding temp string to temp line
so basically TempS is going to contain what it had before plus temp L and then
I'm going to add a line break which is represented by this variable so this
represents a return character which is a line break okay so now we're going to
keep looping this and then I'm going to close the file
and the last thing I want to do is I want to display everything in TempS
which is going to contain the whole file into the label so Label1.Text is
going to equal TempS okay now I want you to now click run to start debugging and
see what happens so save it first ctrl s click the play button or debug button
and then you will see the application with a button you can press so press
that button and you will see an error what is the error it cannot find your
text file so that is all part of the plan
so now we're going to copy this file path and I'm going to open up this file
this folder according to that path so that path is
located here all right so I've just opened it up from my computer and within
this folder I'm going to right-click and create a txt files a new text document
and I'm going to call it score.txt and what am I going to put in this file all
right now I'm just going to put in my name and let's say a score
that I got from Tetris or whatever game that I have played and then I might do
it for my brother as well okay so I'm going to save this file close it close
this folder I'm going to stop it and I'm going to run this file run this program
again and this time when I click read from file
it reads my text file and puts it in the label okay so hopefully you got
something out of this tutorial see you again next time.