Debugging, Static Variables, ByRef, ByValue Chapt. 6 in Deitel, Deitel and Nieto.
Variables and DeBugging
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Transcript of Variables and DeBugging
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
FRUIT$ POOL.LENGTH LAST_NAME$ BIRTHDATE$ AGE
1FRUIT$ F$ FRUIT TYPE$ FRUIT*$ NEWFRUIT$ FRUIT
Good Naming Examples Poor Naming Examples
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 #1:
LET 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 #2:
LET 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 Errors Most common error Programmer violates the grammatical rules of
Qbasic Error message will be displayed at bottom of screen
Logical Errors Program may stop executing prematurely Program may execute completely, but produce
incorrect results Mathematical errors Formatting errors
Debugging Practice
1. Debugging exercise #1 – complete and we will go over as a class
2. Debugging exercise #2 – complete and turn in for a grade