In the previous tutorial we learned the core essentials of writing batch files.

If you have no clue what batch is, but want to learn it, refer to the "Very Basic Batch Tutorial".

In this tutorial you will learn more advanced commands and how to use them to create an application.

Step 1: Variables Step (1/3)

Variables are things that are subject change.
When we create a variable, we are creating something that we want the computer to remember for us, something that we can use later on in a program;
we give the computer the value that we want to store and we give it a label to store it under.

we can create integers and strings using variables.

To create a variable you need to learn the SET command.

The SET command is what creates variables;

SET name=value

Type the following into your CMD:
SET name=hello

'name' is the name of the variable, and 'hello' is what the variable is storing

so now every time you type "echo name" it should say "hello" yes?
NO

if you want to display a variable you must put percentage (%) signs around it.

So therefore if you type "echo %test%" and it should say "hello" yes?
YES

Step 2: Variables Step (2/3)

So now surely we can do maths?

we type
set num=1
This creates a variable called "num" with a value of 1 attached to it.

then
set num=%num%+1
(this means that we take "num" (aka 1) and make it num+1 (aka 1+1))

then
echo %num%
it should give us 2, right?

let's try it:
type the following in notepad and save as MathAttempt.bat
(do not include the stars (*))
@echo off
set v=1
set v=%v%+1
echo %v%
pause
it should say 2, yes?
NOPE.
it says 1+1

because the computer interprets your command as:
you: "so num=1, right?"
pc: "right"
you: "so what is num plus one?"
pc: num+1 = 1+1
so the computer interprets your command literally.

Step 3: Variables Step (3/3)

So how do we get the computer to think mathematically?
Simple, we add an /a before the variable name

For example:

we type
"set /a num=1"

then
"set /a num=%num%+1"

then
"echo %num%"

then we should get 2, right?
let's try it
Type this into notepad....blah blah blah, you know the drill.
***************************************************
@echo off
set /a num=1
set /a num=%num%+1
echo %num%
pause
****************************************************
there! it added 1+1!
this is how the computer sees it:
_
you: so num=1, right?
pc: right
you: so what is num plus one?
pc: num+1 = 1+1 = 2
Voila!

So now lets make a counting program!
we will use the goto command that we learned about in the Very Basic Batch Tutorial.

*********************************************************
@echo off
set /a num=1
:top
set /a num=%num%+1
echo %num%
goto top
**********************************************************
The computer is adding 1, then going to the top and adding 1 again etc.

Step 4: Parameters Step (1/2)

So now that we can use variables what if we have a choice of options, like:
press 1 to say Hello.
press 2 to say Goodbye.

We use the "IF" command, for example:

Type this in your CMD:
if 1==1 echo See it works!
(==) means "is equal to", you could also type "EQU")
We got a message saying "See it works!"

Now type this:
if 1==2 echo It Works!
We didn't see anything because 1 does not equal 2

If we want to wait for the user to put something in we add a /p and leave the part after the variable empty.

Like this:
set /p variablename=

That means that the computer will wait for you to put in something.

so we type:
**************************************
@echo off
set v1=hi!!
set v2=bye!!
echo Press 1 to say HI!
echo Press 2 to say BYE!
set /p you=
if %you%==1 echo %v1%
if %you%==2 echo %v2%
pause
**************************************
This is telling the computer that if we type 1, it must echo HI!, and if we say 2 it must echo BYE!!

Step 5: Parameters Step (2/2)

So now we know that if we want to choose a variable we type:
set /p variablename=

and if we want to set a variable, we type:
set /a variablename=value

So now why not make a little program that counts to and from 2000?
We will use SET, IF and GOTO in this program (and obviously echo)
*************************************
@echo off
set /a num=0

:top
set /a num=%num%+1
echo %num%
if %num%==2000 goto goback
goto top

:goback
set /a num=%num%-1
echo %num%
if %num%==0 goto top
goto goback
**************************************
So now, whenever it reaches 2000, the IF command makes it GOTO the second part which makes it count down, then when it reaches 0, it will GOTO the first part which makes it count up...etc etc etc

Step 6: Done

You have finished my batch tutorials.
You can go here to go to another instructable for some Cool Batch Applications

If you would like help with any of your Batch programs, message me or send me an e-mail at jbell@live.co.za and I will try to help you.

If you want to try something offline, I recommend getting Learn Batch File Programming! by John Albert, really simple, easy to follow and great if you want to get better!