VARIABLES AND
DEBUGGING
Beginning Programming
Assignment Statements

Used to hold values in a variable
Calculates a result and stores it in a variable

Variable: used to hold values in a program

 Should
describe what it holds
 Starts with a letter
 Cannot use spaces
 Can only use _ , $ , and .
 Cannot use reserved words (such as RUN, NEW, PRINT, etc.)
 Should end a string (a sequence of characters enclosed in
quotation marks) with $
Variable Naming
Good Naming Examples





FRUIT$
POOL.LENGTH
LAST_NAME$
BIRTHDATE$
AGE
Poor Naming Examples






1FRUIT$
F$
FRUIT TYPE$
FRUIT*$
NEWFRUIT$
FRUIT
Practice


Complete the Creating Descriptive Variable names
worksheet
Complete the Storage Location Worksheet
Commenting Variables in REM
Statements




You need to list every variable that you use in the
program in your REM Statements
You will put there in the Variable Declaration section of
the REM Template
You should list the variable name and then describe
what the variable stands for
Example:
 REM
POOL.LENGTH holds the length of the pool in feet
 REM TEACHER_NAME$ holds the teachers first and last
name
Assignment

Complete REM and Variable Practice Worksheet
Using Variables in the Main Program

To set the value of a variable, use the command LET
 Examples:
 LET
Stage.Length = 5
 LET Subject_Name$ = “Algebra”

You can also set the value of the variable without
the word LET
 Examples:
 Stage.Length
=5
 Subject_Name$ = “Algebra”
Using Variables in Processes

You will want to use variable names when solving
equations
 Example
 LET
#1:
Length = 5
 LET Width = 4
 LET Height = 3
 LET Volume = Length * Width * Height
 PRINT “The volume is “; Volume; “.”
Using Variables in Processes

You will want to use variable names when solving
equations
 Example
 LET
#2:
First.Name$ = “Bob”
 LET Last.Name$ = “Smith”
 Customer.Name$ = First.Name$ + “ “ + Last.Name
 PRINT “The customer’s name is “; Customer.Name$
Some important facts


Try to use variables whenever you can and have the
computer solve mathematical equations for you,
rather than solving them yourself. If you solve them
yourself and just enter the answer, you will have to
do it all over again if you want to run the program
with different input numbers.
In PRINT statements, remember to separate the
parts in quotations with the variables not in
quotations with a ;
Assignment
Program #4A
Debugging

Debugging: Figuring out the errors in a program

There are 2 types:
 Syntax



Most common error
Programmer violates the grammatical rules of Qbasic
Error message will be displayed at bottom of screen
 Logical


Errors
Errors
Program may stop executing prematurely
Program may execute completely, but produce incorrect results
 Mathematical errors
 Formatting errors
Debugging Practice
1.
2.
Debugging exercise #1 – complete and we
will go over as a class
Debugging exercise #2 – complete and turn
in for a grade