A Minimal Snap Extension to Improve the Treatment of Integer

Data: A Constructionist Approach

Maria Cristina Carrisi

Dipartimento di Matematica e Informatica, Università degli Studi di Cagliari, Via Ospedale 72, Cagliari, Italy

Keywords: Constructionism, Computational Pedagogy, Visual Programming, Numerical Sets, Arithmetic Operations.

Abstract: Block based programming environments are a fundamental resource in introducing students to coding, an

activity that has been proven to be useful in the development of competences laying in the field of mathematics.

Unfortunately, it has been recently shown that Scratch, the most famous and diffused among those languages,

presents an important lack in the treatment of Integer data: it does not provide easy and intuitive instruments

to face problems dealing with the division with remainder. This conflicts with Scratch’s aim and could also

bring students to create misconceptions about the division operation. For this reason, a minimal Snap

extension will be here proposed, which overcomes this problem by creating a block environment more

pertinent from a mathematical perspective.

1 INTRODUCTION

Constructionism (Harel and Papert, 1991), a learning

theory based on constructivism (Kelly, 1955; Piaget

and Inhelder, 1969), focuses on learners’ experience.

Students learn from everyday experiences or from

activities appropriately built by the teacher and

reflecting on them. Teachers should start from pre-

conceptions or from the naive conceptions that

students spontaneously create by observing the

surrounding world and help them formalize or

generalize correctly.

In this pedagogical framework meaningful

activities are to be preferred like

• hands-on activities in which learners build

something (an object, a video, a computer

application, a tale) that can be experienced by

others (Harel and Papert, 1991),

• problem-solving activities based on reality tasks

(Jonassen, 1994).

Activities take place in a specific learning

environment which can be a physical place

(laboratory, museum, garden), a situation or a digital

environment. Students are free to use all the tools at

their disposal to solve the problem, without limiting

themselves to the simple repetition of a known

procedure. This means that in the design and

https://orcid.org/0000-0002-2837-3971

construction of learning activities, it is essential that

teachers create or use learning environments that are

not misleading and do not lead students to create

misconceptions.

If a digital environment is used, it must have a

simple interface and must be usable in an intuitive

way without any specific training.

Block programming environments lay in this

pedagogical context. Their main objective is to allow

a simple approach to computer programming:

overcoming the problem of knowing the syntax of a

given language, it is possible to focus exclusively on

the algorithm and on the resolution process.

Designed in 2007, Scratch (Resnick et al., 2009)

is the youngest and probably the most famous among

them (http://scratch.mit.edu/). It was initially

conceived to introduce children to coding, but in

recent years Scratch has proved to be a powerful

instrument also for adults who have no previous

experience in computer programming (Malan and

Leitner, 2007; Federici, 2011; Homer and Noble,

2017; Weintrop and Wilensky, 2017).

Moreover, Scratch revealed to be an environment

that allows the development of abilities laying in the

context of other subjects (see for example Federici et

al., 2019) and, in this sense, it is a powerful tool also

for teachers of disciplines that are not necessarily

technical or scientific.

Carrisi, M.

A Minimal Snap Extension to Improve the Treatment of Integer Data: A Constructionist Approach.

DOI: 10.5220/0010476103030310

In Proceedings of the 13th International Conference on Computer Supported Education (CSEDU 2021) - Volume 2, pages 303-310

ISBN: 978-989-758-502-9

303

What about Mathematics?

An interesting perspective (Mor and Noss, 2008)

is that coding represents the link between

mathematics and narrative. In this sense it allows to

contextualize and give meaning to mathematics and

visual environments like Scratch can empower the

narrative aspect of computer programming.

Moreover, the literature shows that there is a

significant correlation between coding activities and

the acquisition or improvement of mathematical skills

such as problem solving, modeling, reasoning (Calao

et al. 2015), but also the ability to argue to motivate

the choices made in the implementation.

Consequently, it could be thought that the use of

some features of Scratch can also help to improve the

understanding of specific mathematical contents, but,

unfortunately, the literature does not exhibit any

evidence in this regard, at least in the knowledge of

the author.

Instead, some studies show that there is an

incorrect transfer and overlap between some

mathematical concepts and the corresponding ones in

computer programming. For example, Guzdial

(Guzdial, 2018) pointed out that students show

difficulties in interpreting the correct meaning of the

‘=’ sign or the fact that, in some programming

environments, variables can change domain (type)

during the program execution. More recently (Carrisi,

2020) it has been shown that some of the most

diffused digital environments, among which Scratch,

manage Integer numbers and arithmetical operations,

in particular the division, in a different way from their

mathematical definition. This can create or reinforce

a misconception regarding the division between

Integers, especially if such environments are used in

primary school when students have not yet created a

solid understanding on numerical sets.

The present paper aims to fill this gap of Scratch,

proposing a possible extension obtained with Snap!,

with two new operators that allow to manage the

division with remainder in a more pertinent way from

a mathematical point of view. In such way an

environment is obtained in which students can move,

explore, try, as prescribed by constructivism, without

the risk of running into something that can generate

incorrect knowledge, at least as regards the division

with remainder.

The article is organized as follows: Section 2

presents an analysis of the Scratch operators from a

mathematical point of view with the aim of motivate

the necessity to introduce the new operators; In

Section 3 the new operators are described and the

advantages of their employment when solving a

problem dealing with the division with remainder are

discussed; Section 4 shows the outcomes of a first

evaluation survey conducted on first year students at

the faculty of Computer Science of the University of

Cagliari; finally, the results are discussed, outlining

limitations and recommendations for future work.

2 AN ANALYSIS OF SCRATCH

FROM A MATHEMATICAL

POINT OF VIEW

Scratch is a visual programming environment in

which graphic objects called "sprites" act on a

background called "stage". Sprites and Stage are

customizable, enhancing user engagement, and can

be controlled by programs created with predefined

blocks, joining them together to create a script. Block

shapes allow them to connect only in a few ways, thus

avoiding syntax errors. The Scratch interface is user

friendly and has a series of sections listing the blocks

belonging to the same topic. Furthermore, in each

section, the blocks are grouped by scope and each

block is named in a way that make immediately

understandable the instruction that will be performed.

An analysis of the Scratch environment with

mathematical lens highlights the presence of a series

of features that could be used to improve

mathematical knowledge, like:

• The presence of an XY grid on the stage that can

be explored through the motion of the sprites

might be used to empower students’ knowledge

about Cartesian coordinates.

• The Pen and Move blocks allow learners to

explore geometric shapes and their properties.

• The Variables blocks can be used to create and

manage variables, introducing students to algebra.

• The Operators section (see Figure 1) contains

arithmetic operators but also logical and relational

operators and mathematical functions.

However, according to Brown (Brown, 2017)

“Programming tools are not pedagogy-neutral”. The

type of instruments the programming environment

provides and the way they work “determines which

programming-related activities are easy and which

are hard, which in turn will affect how” a teacher “use

the tool to teach” and what and how students learn.

Recently, (Carrisi, 2020) Scratch has been

analysed under this perspective, particularly focusing

on variables and on the tools that allow to calculate a

division. It is important to underline that the division

is an operation defined in all numerical sets but,

despite the same name, it has different meaning and

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properties depending on the numbers it is working on.

When we consider two Integer numbers a and b,

the division, or more properly the division with

remainder, between a and b gives two Integer

numbers q (quotient) and r (remainder) such that

a=b*q+r, r is positive and lower than b.

When we move to Rational numbers the division

takes on a different meaning and it becomes an

operation that gives a unique result.

Figure 1: Scratch Operators section.

Since, for the sake of simplicity, Scratch variables

cannot be typed, numbers and arithmetic operators

are defined in the floating-point set (a subset of

Rational numbers). The division operator ‘/’ always

gives a decimal result.

The calculation of quotient and remainder of a

division between two Integer numbers is a more

difficult task.

The remainder is given by the ‘mod’ operator

which, however, works differently from its

mathematical definition, in fact it acts also on decimal

data giving a decimal result, as we can see in the

following Figure 2.

Figure 2: Scratch ‘mod’ block working on rational data.

There is no specific operator to obtain the

quotient. It could be argued that there is no need for

it because the quotient can be obtained simply by

approximation of the decimal result of the division.

Scratch provides three different operators to

approximate: ‘floor’ truncate the decimal part of the

number, ‘ceiling’ performs an upper approximation,

‘round’ behaves as ‘floor’ when the decimal part of

the number is less than 0.5 and as ‘ceiling’ otherwise.

The last is immediately visible in the Operators

section while the first two are accessible through a

dropdown menu contained in the last operator of the

section (see Figure 1 and Figure 3).

Figure 3: The ‘floor’ and ‘ceiling’ operators.

The blocks ‘mod’ and ‘round’ are grouped like the

relational operators or the logical connectives (see

Figure 1). This induces the user to think that they are

logically related and referred respectively to

remainder and quotient of an Integer division, but it

is not correct as we can see in the example reported

in the following Figure 4.

In order to obtain the correct quotient of a division

between two integer numbers (see Figure 5) it is

necessary to truncate the decimal result of the

division, by using the ‘floor’ block that, as just

stressed, is hidden in the dropdown menu and so its

use is much less intuitive.

A Minimal Snap Extension to Improve the Treatment of Integer Data: A Constructionist Approach

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Figure 4: Incorrect use of Scratch blocks ‘mod’ and ‘round’ to calculate a division with remainder.

Figure 5: Correct use of Scratch blocks ‘mod’ and ‘floor’ to calculate a division with remainder.

The interpretation and calculation of the division

with remainder turn out to be a cumbersome, and not

at all intuitive, operation, even for how the interface

is designed.

2.1 Analysis of a Particular Problem

Let’s consider the following problem (Carrisi, 2020):

Problem: In a supermarket, the following sales

promotion is active on a certain product: if you buy

three products of the same type, only two must be paid

for. If the number of products purchased and the price

of the individual product are known, what is the total

purchase price?

The above problem can be proposed at all school

levels (see for example the Italian school curricula

MIUR, 2010; MIUR, 2013; MIUR, 2018) and can be

solved by using different methods and learning

environments.

A possibility is to come to an algebraic

formulation like the following: P = (2 * q + r) * p.

P is the final price, considering the sale

promotion. N is the number of products bought and p

is the price of the single product. q is the quotient of

the division of N by 3 and represents the quantity of

groups of three products. For each group, only two

products must be paid. r is the remainder of the

division of N by 3 and identifies the number of

products that must be paid entirely.

Otherwise, we can calculate P = (N – q) * p where

the variables have the same meaning reported above.

In this case we are subtracting the discount from the

total price. The discount amounts to the price of one

product for each group of 3 products, given by q.

In both cases it is necessary to calculate the

quotient of the division with all the difficulties

evidenced in the previous section if the chosen

learning environment is Scratch.

In Figure 6, reported in the subsequent page, we

see the Scratch implementation of the first solution

proposed.

We see that, it is necessary to do data casting to

avoid incorrect data entry (ensures that the number of

products is an Integer number) and allow the

functions to work properly. This, together with the

considerations exposed in the previous section, makes

evident that the mathematical tools under

consideration are not adequate, from a constructionist

point of view, to properly manage the operation of

division with remainder and this conflicts with

Scratch pedagogical background.

It could be said that this is not very interesting

from the point of view of teaching-learning because

the division with remainder is an operation poorly

used and that the problems in which it is necessary its

use have little application value. The literature shows

that it is not the case.

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Figure 6: Scratch solution of the Problem.

In a recent paper (Dogan and Ev Cimen, 2019) the

authors pointed out that “the division is the most

difficult for students, compared to the other

operations” especially because of the different

meaning that the operation, the data and the results

may take depending on the context. They also proved

that problems dealing with the division with

remainder are difficult for children, but also for

elementary teachers, precisely because the resolution

is closely related to the interpretation and

contextualization of the problem. This means that

they are particularly appropriate from a

constructionist perspective, as they can be used to

present a wide range of reality tasks. Moreover, they

focus on problem solving procedure more than

computation, enhance the ability of analyse the

domain of data, the presence of eventual constraints,

and of interpret results, all features deemed necessary

for the mathematics of the future because they

complement computers’ “abilities” (Gravemeijer et

al., 2017).

For these reasons, it seems necessary to extend

Scratch adding new operators that make the

calculation of the division with the remainder more

intuitive and mathematically relevant for the students,

especially if they belong to primary school.

3 A SNAP! EXTENSION

Although Scratch is equipped with a large series of

instruments, at a certain time the community has felt

the necessity to extend its capability by adding or

modifying some components. Such modifications

("mods") have been possible thanks to the fact that

Scratch is an open source project and so its source

code is freely available. Mods expand the language,

adding suitable operators to manage more advanced

computational concepts ore including functionalities

like the possibility to communicate with hardware

devices (e.g. Microsoft Kinect), or to build web pages

in a simpler way (e.g. Web Blox). The first Scratch

mod is BYOB, now known as Snap! (Harvey and

Monig, 2010). It has a fundamental add-in: the

possibility to define new customized blocks,

remaining fully compatible with Scratch.

Snap! interface looks like Scratch’s one, except

for the presence of much more blocks. At the bottom

of each section, there is a grey button ‘Make a block’

that gives the opportunity to the user to create a

customized block belonging to a category already

defined or completely new. The new block may be a

command, a reporter (returns a result) or a predicate

(returns a truth value).

The behaviour of the new operators can be

implemented by using Snap! primitives (the existing

blocks) and the usual drag and drop procedure.

See the user’s manual for more details:

https://snap.berkeley.edu/snap/help/SnapManual.

pdf

With the aim to solve the problems evidenced in

the previous section, two new reporter blocks have

been created in the ‘Operators’ category (see Figure

7 in the following page).

A Minimal Snap Extension to Improve the Treatment of Integer Data: A Constructionist Approach

307

Figure 7: Overview of the Operators section with the new

elements.

The first operator, called ‘Quotient’, receives two

Integer numbers n1 and n2 and returns the quotient of

the division between n1 and n2. To prevent incorrect

data entry, the parameters n1 and n2 are cast by

truncation.

Figure 8: Implementation of the Quotient operator.

In Figure 8 we can see the implementation of the

operator while in Figure 9 it is shown how this

operator works on Integer parameter as well as on

Rational numbers.

Figure 9: Quotient operator acting on Integer data and on

Rational data.

The second operator, called ‘Remainder’ receives

two Integer numbers n1 and n2 and returns the

quotient of the division between n1 and n2. In fact, as

it can be seen in Figure 10 and similarly to the

‘Quotient’ operator the parameters n1 and n2 are cast

by truncation.

Figure 10: Implementation of the Remainder Operator.

It is clearly just an adjustment of the ‘mod’

operator but that makes the operator resistant to

incorrect data entry and adherent to its

mathematically meaning.

In building the operators we were inspired by

strongly typed programming languages like C, in

which the assignment of a decimal value to an Integer

variable produces a truncation.

The implementation of the solving algorithm for

the Problem analysed in the previous section, with the

use of the new operators becomes surely more

adherent to its algebraic formulation as we can see in

the Figure 11 in the subsequent page.

4 EVALUATION

A fist evaluation of the new operators that

investigates students’ acceptance has been carried out

in the last months of 2020.

For the reasons behind this research, the author’s

initial intention was to carry out activities with

elementary school students and then conduct a

survey. This was made impossible by the restrictions

imposed by the Covid-19 pandemic that banned the

access of external staff in schools. It was not even

possible to carry out activities remotely as pupils are

already undergoing a large number of hours of

distance teaching.

Consequently, since the purpose was to evaluate a

programming environment, it has been chosen to

involve in the survey the students of the first year at

the faculty of Computer Science of the University of

Cagliari. with whom, given their age, it has been

possible to carry out activities remotely.

Initially, the problem presented in Section 2.1 was

proposed to students and asked them to upload their

complete solution of all steps.

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Figure 11: The solution of Problem obtained with the Snap! extension.

102 students participated to this first part of the

activity: 58 of them solved the problem correctly and

giving a general solution; 9 were able to produce only

a particular solution valid in the case N multiple of 3;

35 were unable to solve the problem (see Figure 12).

Figure 12: Distribution of students responses.

In the second part of the activity, after correction

of the Problem, students were asked to implement the

algorithm in Snap! and in the modified Snap! with the

two new operators. In the end they were offered a

short questionnaire on the perceived effectiveness of

the new operators.

Figure 13: Outcomes of the evaluation survey.

37 on the 58 students that were able to solve the

problem decided to participate answering to the

following questions:

Q1: Is it natural for you to interpret division between

integers as division with remainder?

Q2: Is it natural for you to interpret the division

between integers as an approximation of a division

between real numbers?

Q3: Do you find that the new operators introduced in

Snap make it more intuitive to use the division with

the rest than in the standard version of Snap?

The results show that the satisfaction with respect

to the new operation is good. As we can see in Figure

13, the 24% declared to be absolutely satisfied by the

new operators and that they make more intuitive the

use of Snap! (at least regarding the problem they

worked on); the 16% was very satisfied; the 46%

sufficiently satisfied; no one was completely

unsatisfied and the remaining 14% express a low

satisfaction. With regard to the latter data, it is

interesting to note that students who have declared a

low satisfaction have also stated that they interpret the

division in the context of Integers with difficulty.

5 DISCUSSION AND FUTURE

WORK

The outcomes reported in the previous section put in

evidence that division with remainder problems are

hostile also for University students making technical

studies. Even if the numbers are low, this is a further

confirmation of what is present in the literature

(Dogan and Ev Cimen, 2019).

According to the introduction of the new

operators we underline that Scratch is a software

designed in a constructivist perspective, and it is built

to allow individual exploration by the student that can

find in an easy way the necessary operators to realize

the resolution algorithm for a certain problem. If the

A Minimal Snap Extension to Improve the Treatment of Integer Data: A Constructionist Approach

309

focus is on the solution process, the student should

not be forced to “bend” the operators to work in a

particular way different from the standard mode. For

this reason, it was deemed necessary to introduce a

new operator in Scratch that makes its use more

suitable for the skills possessed by primary school

students especially in the implementation of

algorithms related to problems in the context of

Integers. Although our first survey shows a high

appreciation, it is considered necessary to strengthen

the evaluation with a study conducted on primary

school students. Moreover, in this study positive

numbers have been treated. As future work, we ain to

extend the analysis also to signed number.

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