KTurtle/C3/Common-Errors-in-KTurtle/English

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Title of the tutorial:

Author: Madhuri Ganapathi


Visual Cue Narration
Slide Number 1 Hello everybody.

Welcome to this tutorial on Common Errors in KTurtle.

Slide Number 2

Learning Objectives

In this tutorial, we will learn about
  • Syntax errors
  • Runtime errors and
  • Logical errors
Slide Number 3

System Requirement

To record this tutorial I am using,

Ubuntu Linux OS version 12.04.

KTurtle version. 0.8.1 beta.

Slide Number 4

Pre-requisites

We assume that you have basic working knowledge of KTurtle

If not,

for relevant tutorials, please visit our website.

http://spoken-tutorial.org

Slide Number 5

Definition of Error

Let's first define, What is an error ?

Error is a mistake in a program that produces an incorrect or unexpected result.

First I will explain about "Types of errors".
Slide Number 5

Syntax Errors

A syntax error is a violation of grammatical rules, of a programming language.

Compilation fails when a program has syntax errors.

Syntax errors are easy to find and fix.

For Example:

  • Unmatched parentheses, square brackets and curly braces.
  • Use of variable that has not been declared.
  • Missing quotes in strings.
Switch to KTurtle Application

Dash home >>In the Search bar type KTurtle

Click on the KTurtle icon.

Let's open a new KTurtle Application.

Click on Dash home. In the Search bar, type KTurtle.

Click on the KTurtle icon.

Let's begin the tutorial with some types of syntax errors.
I already have a program in a text editor.
Comment code To explain the error in the program, I will comment part of the code.
Highlight

$a=ask "enter any number and click Ok"

Here, I will comment the line

$a=ask within double quotes "enter any number and click Ok"

Type # I will use hash(#) sign to comment the line.
reset

#$a=ask "enter any number and click ok"

print $a^3'

spritehide

I will copy the program from text editor and paste it into Kturtle's Editor.

Pause the tutorial here and type the program your into KTurtle editor

Resume the tutorial after typing the program.

Run the program Let's click on Run button to run the program

Complier shows the following error,

variable "$a" was used without first being assigned to a value.

Highlight Line number 4 Here the error is in line number 4.
Syntax error This is a syntax error. It occured, as the variable 'a' was not declared.
Highlight $a=ask "enter any number and click Ok"

Remove the comment

So I will go to line number 2 remove the comment.
reset

$a=ask "enter a number and click ok"

print $a^3

spritehide

I will copy the program from text Editor and paste it into KTurtle's editor.
Run the program Let's click on Run button to run the program

Enter 6 for a value and click OK

Program runs without errors.

clear command I will clear the current program from KTurtle editor.

Type clear command and Run to clean the canvas.

let's next look about another error.
I already have a program in a text editor.
Highlight

$radian=(pi/180)*$degree

Here the value of "pi" is predefined in KTurtle.
Highlight $ Let's delete the "$" sign in the program.
reset

degree=ask "enter an angle value and click OK"

$radian=(pi/180)*$degree

go 50,50

print "Value in radians is"+ " " +$radian

spritehide

I will copy the program from text editor and paste it into Kturtle's Editor

Pause the tutorial and type the program your into KTurtle editor


Resume the tutorial after typing the program.

Run the program Let's Click on Run button to run the program.

Complier shows the following error,

you cannot put “=” here

Highlight Line number 2 This error is in line number 2.
Show error This is a syntax error it occured, as there is no container of variable.
Replace $ sign Let's go back to the program replace the $ sign.
reset

$degree=ask "enter an angle value and click OK"

$radian=(pi/180)*$degree

go 50,50

print "Value in radians is"+ " " +$radian

spritehide

I will copy the program from text editor and paste it into KTurtle's Editor
Run the program let's click on Run button to run the program.

Enter 45 for angle value and click OK

Program runs without errors.

Highlight "enter an angle value and click OK" Let's remove one of the quotes of the string.
reset

$degree=ask "enter an angle value and click OK

$radian=(pi/180)*$degree

go 50,50

print "Value in radians is"+ " " +$radian

spritehide

I will Copy the program from text editor and paste it into KTurtle's Editor
Run the program Click on Run button to run the program

Complier shows the following error,

Text string was not properly closed, expected a double quote “ ” to close the string.

Highlight Line number 2 Here the error is in line number 2.
Replace the quotes I will go to line number 2 and replace the quotes.
reset

$degree=ask "enter an angle value and click OK"

$radian=(pi/180)*$degree

go 50,50

print "Value in radians is"+ " " +$radian

spritehide

I will copy the program from text editor and paste it into Kturtle's Editor

Run the program Click on Run button to run the program

Enter 45 for angle value and click OK.

Program runs without errors.

This way you can find the line at which error has occured, and also correct it.

Let's now learn about runtime errors.
Slide Number 6

Runtime errors

Run-time error occurs during the execution of a program.

It may crash the program when you run it.

Runtime errors are commonly due to wrong input from the user.

Compiler cannnot find these errors.

For example:

  • Trying to divide by a variable that contains no value.
  • Run a loop without a terminating condition or increment value.
“clear” command' I will clear the current program from the KTurtle editor.

Type clear command and Run to clean the canvas.

Highlight the program I already have a program in a text editor.

This program divides two numbers.

'a' is dividend and 'r' is divisor.

reset

$a=ask "enter a number for 'a' and click Ok"'

$r = ask "enter a number for 'r' and click OK"

$d=$a/$r

print $d

I will copy the program from text editor and paste it into KTurtle's Editor.

Pause the tutorial and type the program into your KTurtle editor

Resume the tutorial after typing the program.

Run the program Let's click on Run button to run the program.

le'ts enter 5 for 'a' and click OK

enter 0 for 'r' and click OK

Here we get a runtime error ,

“you tried to divide by zero”

Highlight Line number 4 This error is in line number 4.
Run time error This error occurs as we cannot divide a number with zero.
Run the program Let's run the program again.

Enter 5 for number and click OK

enter 2 for 'r' and click OK

Program without errors.

“clear” command I will clear the current program from KTurtle editor.

Type clear command and Run to clean the canvas.

Next we will learn about logical errors.
Logical errors Logical error is a mistake in a program's source code that results in incorrect or unexpected behavior.

For example,

Assigning a value to the wrong variable.

Multiplying two numbers instead of adding.

I already have a program in a text editor.
reset

$x=30

message"In while loop, code inside the loop repeats till boolean

evaluates false"

while $x>20 {

$x=$x+1

fontsize 15

forward 20

print $x }

I will copy the program from text editor and paste it into Kturtle's Editor

Pause the tutorial here and type the program into your KTurtle editor

Resume the tutorial after typing the program.

Run the program Now click on the Run button to run the program.

A dialog box pops-up, let's click OK.

Loop goes into an infinite loop.

Highlight “ while” loop condition We see that “while” loop prints numbers from 31 and it is still printing.

This is a logical error.

In the “while” condition x is greater than 20,

but the variable x is always greater than 20

So, the loop never terminates.

Abort the process I will click on Abort button to abort the process.
Change $x=$x+1 to $x=$x-1 Let's change $x=$x+1 to $x=$x-1.
reset

$x=30

message"In while loop, code inside the loop repeats till boolean evaluates false"

while $x>20 {

'$x=$x-1'

fontsize 15

forward 20

print $x }

I will copy the program from text editor and paste it into KTurtle's editor.
Run the program Let's click on Run button to run the program.

A dialog box pop-up let's click OK.

Loop terminates after printing values from 29 to 20.

With this we have come to the end of this tutorial.

Let us summarise.

Slide Number 9

Summary

In this tutorial we have learnt, errors and types of errors such as
  • Use of variable that has not been declared.
  • Missing quotes in strings.
  • Runtime errors and
  • Logical errors
Slide Number 10

Assignment

As an assignment I would like you to find errors in the given programs
Assignment 1 reset

$x=3

$y=3

if $x==$y

print"they are equal"

else {

print "they are not equal"}

Assignment 2 program to find the nth term and sum of n terms in GP

reset

$x=ask "enter value for x and click Ok"

$y = ask "enter value for y and click Ok"

$g =sqrt ($x*$y)

print "Geometric mean is ="+

Assignment 3 reset

learn sum $x {

{$r=0

for $i= 1 to $x{

return $r}

}

print

Slide number 11

Acknowledgement

Watch the video available at this URL

http://spoken-tutorial.org/What is a Spoken Tutorial It summarises the Spoken Tutorial project If you do not have good bandwidth, you can download and watch it

Slide Number 12

The Spoken Tutorial Project Team :

Conducts workshops using spoken tutorials Gives certificates to those who pass an online test For more details, please write to contact@spoken-tutorial.org

Slide number 13 Spoken Tutorial Project is a part of the Talk to a Teacher project

It is supported by the National Mission on Education through ICT, MHRD, Government of India More information on this Mission is available at this link http://spoken-tutorial.org/NMEICT-Intro ]

This is Madhuri Ganpathi from IIT Bombay signing off. Thank you for joining

Contributors and Content Editors

Arya Ratish, Madhurig

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