Mathematical Calculations

Mathematical Calculations

Q-BASIC Zero Day Code Ananlysis   00:40

QBasic was obviously created for us to have fun, play games, draw nice graphics and even make sounds.

But, as you might guess, nothing good comes without a bit of effort that has to be put in it. In the most QBasic programs a bit of math has to be done.

The math… Doh!

If you hate mathematics, don’t worry. QBasic will do it all for you, you just need to know how to tell
QBasic to do that.


QBasic can perform the following mathematical operations:

Operator	What it does	Example	Result
+	Add	7 + 2	9
-	Subtract	7 – 2	5
*	Multiply	7 * 2	14
/	Divide	7 / 2	3.5

Examples:

1.  a = 15 / 4 + 3
    PRINT a
    Result on the screen – 6

2. PRINT “Enter the first number”
    INPUT a
    PRINT “Enter the second number”
    INPUT b
    c = a + b
    d = a * b
    PRINT a; “+”; b; “=”; c
    PRINT a; “*”; b; “=”; d
    END

When you run this program it goes like this:

Computer: Enter the first number
You: 22
Computer: Enter the second number
You: 18
Computer: 22 + 18 = 40
22 * 18 = 396

Advanced operations:

Operator	What it does	Example	Result
\	divides and turns the result into an integer (the whole number)	7 \ 2	3
^	Raises a number to the power of another number	3 ^ 4 (means: 3 * 3 * 3 * 3) 2.5 ^ 3 (means:2.5 * 2.5 * 2.5)	243 15.625
SQR	Calculates the square root of a number	SQR(9)   SQR(16) SQR(5)	(because:  3 ^ 2 = 9) 4 (because:  4 ^ 2 = 16) 2.236
MOD	Divides two numbers, and if the result is not an integer (for example - 3.25), finds out how much to subtract from the first number in order to get the integer result.	17 MOD 5	2 (because:  17 / 5 = 3.4 17 – 2 = 15 15 / 5 = 3)

The following program explains MOD. Type this program (except my comments) into QBasic accurately and run it to see how MOD works.

1 CLS                                       this command clears the screen, so it’s empty
INPUT "Enter the first number "; a
INPUT "Enter the second number "; b
IF b = 0 THEN         checks if the second number is zero, because you can’t divide by zero
PRINT "the second number cannot be 0. Try again."
DO: LOOP WHILE INKEY$ = ""   waits for you to press a key to continue
GOTO 1                                  then sends you back to line 1
END IF
CLS                                       clear the screen again
c = a MOD b
d = a / b
e = a - c
f = e / b
PRINT a; "MOD"; b; "="; c
IF c = 0 THEN        this checks if the result of a MOD b = 0, because it means that  the result of a / b is                                          integer
PRINT "because"; a; "/"; b; "="; d; " - integer. Try again."
DO: LOOP WHILE INKEY$ = ""   waits for you to press a key to continue
GOTO 1                                     then sends you back to the line 1
END IF
PRINT "because"; a; "/"; b; "="; d; " -not integer"
                                                                       The rest of the program executes if the
PRINT "but"; a; "-"; c; "="; e      result of a / b is not integer
PRINT "and"; e; "/"; b; "="; f; " - integer"
END

This program may look very complicated for you, but don’t worry. QBasic is a very easy language to learn and soon you’ll be having fun with it. 
I promise you!

Variables

Variables

Q-BASIC Zero Day Code Ananlysis   03:08

                                               Variables
When you think, you keep words or numbers in your mind. This allows you to speak and to make calculations.

QBasic also needs to keep words or numbers in its memory. To do this, you use variables, pieces of QBasic memory, which can keep information. A variable can be named with any letter, 
for example – 

a. It can also have a longer name, which can be almost any word. It is important to know that there are two main types of variables – that keep a number and that keep a word or a string of words.

• Numeric variables. It’s basically variables named with just a letter or a word. You tell this variable to keep a number like this:

a = 15

In other words, you assigned the value 15 to the variable a.
QBasic will now know that the variable named a keeps the number 15. Now, if you type

PRINT a  

and run the program, the computer will show this number on the screen.

• String variables can keep so called “strings”, which is basically any text or symbols (like % or £), which you put in the quotes “ ”. You can also put numbers in a string variable, but again, you must include them in quotes, and QBasic will think that those numbers are just a part of text. The string variables look like this – a$. The $ sign tells QBasic that this variable contains text.

Example:

a$ = “It is nice to see you”
PRINT a$

On the screen you’ll see:
It is nice to see you

The PRINT command can print more that one string on the line. To do this, put the ; sign between the variables.

For example, you have two variables – name$, which contains name Rob, and age, which contains the number 34. Then, to print both name and age, you type:

PRINT “Name - ”; name$; “. Age - ”; age

NOTE - As you can see, the name of a variable can be more than just one letter – it can be a short word which describes what sort of information does this variable keep.

What you see on the screen when you run the program will look like this:

Name – Rob. Age – 34

Or, you can type the program like that:

PRINT “Name - ”; name$
PRINT “Age - ”; age

The result is:

Name – Rob
Age - 34

GOTO

GOTO

Q-BASIC Zero Day Code Ananlysis   00:12

Quite often you don’t want the program to run exactly in the order you put the lines, from the first to the last. Sometimes you want the program to jump to a particular line. 

For example, your program asks the user to guess a particular number:

******** ‘some of the program here
INPUT “Guess the number”; n
******** ‘some of the program there

The program then checks if the entered number is correct. But if the user gives the wrong answer, you may want to let him try again. So you use the command GOTO, which moves the program back to the line where the question is asked. But first, to show QBasic where to go, you must “label” that line with a number:

1 INPUT “Guess the number”; n         ‘this line is labelled with number 1

Then, when you want the program to return to that line, you type 

GOTO 1

You can use GOTO to jump not only back but also forward, to any line you want. Always remember to label that line. You can have more than one label, but in that case they should be different.

INPUT

INPUT

Q-BASIC Zero Day Code Ananlysis   00:07

INPUT is a command that allows you or anybody else who runs the program to enter the information (text or number) when the program is already running. This command waits for the user to enter the information and then assigns this information to a variable. Since there are two types of variables, the INPUT command may look like this – 

INPUT a (for a number), or INPUT a$ (for a string).

Example (Type this program into QBasic and run it by pressing F5)

PRINT “What is your name?”
INPUT name$
PRINT “Hi, ”; name$; “, nice to see you!”
PRINT “How old are you?”
INPUT age
PRINT “So you are ”; age; “ years old!”

END

Note: The END command tells QBasic that the program ends here.
You don’t have to use PRINT to ask the user to enter the information. Instead, you can use

INPUT “Enter your name”; name$
and the result will be the same.

PRINT

PRINT

Q-BASIC Zero Day Code Ananlysis   00:02

When you open QBasic, you see a blue screen where you can type your program. Let’s begin with the QBasic commands that are important in any program.

                                               PRINT
Command PRINT displays text or numbers on the screen.
The program line looks like this:
PRINT “My name is Nick.”

Type the bolded text into QBasic and press F5 to run the program. On the screen you’ll see 
My name is Abhijeet.

Note: you must put the text in quotes, like this – “text”. The text in quotes is called a string.

If you put the PRINT alone, without any text, it will just put an empty line.
PRINT can also put numbers on the screen.

PRINT 57 will show the number 57. This command is useful for displaying the result of mathematical calculations. But for calculations, as well as for other things in the program, you need to use variables.

QBASIC REMINDER

QBASIC REMINDER

Q-BASIC Zero Day Code Ananlysis   23:37

 A QBASIC program consists of lines containing..

1.  A line number 
2.  A QBASIC keyword like PRINT,END etc 
3.  Each program line begins with positive number. 
4.  No two lines should have same number. 

 RUNNING A PROGRAM 

RUN is the command used to execute the program and get the output on the screen. 

                                   WRITING A NEW PROGRAM 
It is possible to overwrite lines with the new statements, but if you want to write a totally new program use a NEW command. 

                                          EXITING QBASIC 
In order to exit the QBASIC program SYSTEM command is used.