AN ANSI C PROGRAMMING. ENVIRONMENT. DESIGNED. FOR
INTRODUCTORY. USE. Stephen N. Freund and Eric S. Roberts. Department of
Computer ...
THETIS:
AN ANSI C PROGRAMMING ENVIRONMENT DESIGNED FOR INTRODUCTORY USE Stephen N. Freund and Eric S. Roberts Department of Computer Science Stanford University
ABSTRACT
As we have reported
Commercially available compilers, particularly those used for languages like ANSI C that have extensive commercial applicability, are not well-suited to students in introductory
the change
computer
note that the concerns
science
sophistication alleviate
that
this
Thetis
courses beginning
problem
use.
system
associated
user interface
and easily
understood
capabilities.
fulfills
provides
a significantly
students
1.
of students
we
undergraduate
with
time
learning
On further
and
discovery:
for
language Pascal
in CS l/CS2.
than
INTRODUCTION
When
the Stanford
its CS l/CS2 strongly
the C-based department,
as more
members,
Ironically, reservations
about
of the lecturers introductory
only
who
would
that
Pascal
students
to adopt
needed
C were
be responsible
There
was little
saw
both
for
there C and
the and
use.
extensive
for students solving
and algorithmic
expressed
more
to master it,
of
their
was
that
time
the more design. “students
debugging
important
from
environment
of
the
provided
of the The
easier
revised
clearer
to use course,
The
Pascal
diagnostics,
that was much
better
a change
in
language—that
of
course
project
tools
specifically Thetis
mythology—was quarter
we decided
computer
christened
introductory Thetis
that the best
was to develop
designed
science after
to address
students.
the sea (C)
That nymph
used on an experimental
1995
and then
adopted
for
basis
the entire
in the spring.
This
paper
and our experiences
using
it at Stanford.
describes
the
in the 2.
it harder
SHORTCOMINGS
OF
their
the learning
EXISTING
earlier problem
time
for
learning.” Permission to copy without fee all or part of this material is granted provided that the copies an? not made or disbibuted for direct commercial advantage, the ACM copyright notice and the tiUe of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise or to republish, requires a fee and/or speeific permission. SIGCSE ’96 2f96 Philadelphia, PA USA Q1996 ACM 0-69791 -757-X/96/0002 ....50.5O
papers
process
[Ruckert93,
is that
languages
most like
C that designed
As a result,
of these
most
for
cater
environment
beginning
have
students
is
been recognized
Schorsch95].
commercial
programmers—are student
COMPILERS
in the programming
not a new one; such shortcomings
issues of problem
less
for
debugger
of introductory
Greek
in winter
The fear, as one lecturer would end up spending and
was much
of inadequate
complicate
make
higher
a function
programmers.
consideration,
to the problem
by using
would
in their
environment.
of the programming
The idea that weaknesses
course
on
of their
errors
It was these factors—not
curriculum than they had in the past. The concerns were focused instead on whether the added complexity imposed C in the introductory
fraction was often
less
adopted
an interactive
project—since
in anyone’s
earlier
seminar
we made an important
was
errors,
and structure
After solution
one or two
that
we
more
to student
the needs
obsolete
C++
to
When
made the difference.
significant
was no doubt
however,
beginning
detected
the syntax
students
for teaching
question
increasingly
Likewise,
to learn
any
level
we had abandoned
a programming
to express
was becoming
to be replaced.
prepare
of
we determined
obscure
frustration
frustration
the C compiler
suited
attitude shared by and outside the
would
a
a larger
of the programming
compiler
and included
work.
people
the decision
courses.
for
students
in year,
relatively
most
it is important foundation.
its initial
spending
down
examination,
than
compiler
constituencies
In particular,
relevant—an both inside
for advanced the
decided
of instruction
of the affected
who felt that the change
more effectively
needed
most
the change.
material
faculty
Science
C as the language
sequence,
supported
many
mind
ANSI
of Computer
so,
course
after
indeed
student
particularly
Department
in 1991 to adopt
were to track
in fact achieved
not without
C-based
Roberts95a],
on the computer
as a result.
indicate
environment
the
teaching
trying
effect
Even
were
code and that the student
simple
and visualization
and instructors
anticipated.
evaluated
that students
for
we set out to accomplish
better
To
and
[Roberts93,
and that we have
we
the
specifically
students
program
the benefits
of
developed
of a C interpreter
debugging,
the goals
a level
do not possess.
designed
consists
editing,
assume
we have
that provides
Reactions
that Thetis
students
environment
The
they
at Stanford,
programming
student
because
science
elsewhere
to C has had a positive
The
in
underlying
compilers—particularly to
for experts compilers
a large rather
audience
of
than novices.
are poorly
suited
to
use.
In our experience, commercial compilers suffer from the following problems when used in an introductory course:
compilers “ The error messages generated by commercial are often uninformative and sometimes misleadittg. New
300
programmers
tend to make
others.
example,
For
certain
omitting
mistakes a required
more
often
than
semicolon
or
right
curly
brace
Unfortunately, by reporting below
is a very
compilers a seemingly
the actual
does
not detect
file.
Expert
where
error
unrelated
mistake.
syntax
the problem
until
understand
novices
error
Although
error several
lines
to address
point
the parser
section,
in the source
practical
the problem
are completely
and know
baffled.
little or no run-time identify bugs that are
error
confusion,
the greatest
logic
that
frustration
are a source
for
system
students
never
pernicious common outside
comes
from
In
the
detects.
because
Even
helpful
to novices,
rarely
errors
the bounds
pointer.
C,
compilers
run-time
such
such
experts
errors
problem
is especially
generate
code to detect
are unwilling
avenues
are available.
would
its goals
decided ●
to pay the cost.
tt’as
pedagogical
that
offer
fact
of
not
run
at
primarily
if
making
debuggers
sophistication.
The
Stanford,
for example,
character
pointer—a
you understand
usually
require
commercial
C compiler
displays
string
representation
how
a high we
use
string
data internally.
goals
many the
“ (k-pedagogical
In
until
depends
pedagogical
end.
While
the
failure
sense,
present
string
data
restricts
the utility
in
an
this
strategy
makes
of the debugging
understandable
good
tools
way
that
are
C’s
of the debugger.
effective ..
w’hetl
environment.
to a large
extent
products
must
all the resources
developed
locally,
available
on
programming
to support
such integration.
environments
advanced
the
machine,
typically
overwhelm and
offer
flexibility.
To
inadvertently
main
language By that
problem
are later
run-time
run
information
of
from
and debugger during
have
limited
compilation.
Interpreters
itself
into
incur
the
access
a single the
no need to achieve
would simplicity
gladly
sacrifice
and reduced
maximum some
run-time
execution
debugging
for
the
to
ensure
that
models,
it
interpreter
was
be unlikely
new ideas in the design et?vironment.
and dynamic
we identified
in the future,
visualization.
Exploring a research
Although
much
the prospect
a strong
For
the relationship
that we develop
and modify.
of a
In the
as experiments.
in exploring
is
to take cslib
would
design,
of
prepared
Because
useful
C
libraries
mask much To
products
interested
We had a team of students the
incentive
interpreter imaginations
tool
of this
of undertaking to implement
and
importantly, extremely
time.
design
3(
fully
the
[Roberts95b].
The
and enthusiasm
there
iri taking
integrated
program
than
idea
for use in the introductory
competent
interested
students-–even
more
teaching
idea in recent memory. the project and sought
greater
Mvho were
Stanford,
level—are science
institutions
penalty
At
project.
computer
an
phase in
efficiency
speed
the
a preliminary
provided
w’itllin
better
conflicting of
seemed
extend
remains
are
by
several
space required
undergraduate
to the
in execution efficiency that makes them inappropriate for writing production code. Introductory students, however, have
debugging
●
program
a significant
between
on
phase. the
By contrast,
simulates
therefore
Because
year,
interpreter.
instructions
process.
per
in teaching
temporarily
programming
that
we were
such research
inte,erated ., success
definitions.
developing features
research
it hard
is CS
of platform.
Our
commercial
to explore
that we could
users need.
the execution
these operations
interpreter
makes
cslib
based
design
a change
well
components
example, this
commercial
machine
as an independent
combines
the
execution.
generates
if
confused
all the
We wanted
process-of
or incompatible
producers
of
several
severe
not
pedagogically
of the program.
technology
generated
interpreter which
incorrect
that beginning
phase is separate system
●
features
more
of feedback
a compiler
compilation
that
understanding
becomes
execution
facing
special
limits
is that compiler
the kind
definition,
these
chooses
successful
systems
to provide
user interfaces
that
The problem
that prohibit
The
student,
complexity
and self-confidence. options
complex
account
who has no use for the added power the
additional
the student
commercial
have
the beginner
represent
programmers
do
which
introductory
representation.
students
for
systems
1200 students
students
cotnpilers offer a bewildering set of options “ Commercial and special features that are useless to the novice and Because their occasionally cause consistency problems.
are
The
which
until
the underlying
important
those
on campus,
on the use of the cslib
Roberts95a],
complexity
understand
[CenterLine95],
we seek,
over
out’ Even
approach depends on the use of libraries
most
[Roberts93,
to
severely
both
C interpreters,
product
to contemplate
both to
reasons:
satisfied
commercial
available
enroll
computer
project,
requirements.
Macintosh.
at Stanford
programming
to the
Apple
it infeasible
our course, we introduce strings as an abstract type very the underlying representation early in the course, deferring close
hardware
CS298
In the end, we
that
CodeCenter
of the features
on the
other of the
of Stanford’s
hardware
to buy
that
if
for the following
system
and our
project
the dimensions
interpreter
a
software
undergraduate
the project
it is possible
courses
sense only
any
and to assess its feasibility.
such as CenterLine’s
data as a hexadecimal
that makes
C represents
level
though
teaching
no existing
represents
particularly
quarter
the proposed
to undertake
There
● Interactive debuggers typically require students to understand advanced cotl cepts before they are ready to is further complicated by the assimilate them. Debugging
that existing
on
so made are, the
scratch
is a major
lightly,
an entire
evaluating
preceding
doing
Building
sure that we understood
“Seminar
science,”
be
from
strategy.
undertaken
we spent
course,
an invalid
checking
be
that
as the shortcomings
of this scale and complexity not
a C interpreter
in lhe
clear
serious
solution
should
refine
identified
Immediately
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ambitious
problem,
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or dereferencing
run-time
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the
BUILD possible
shortcomings
sense.
system
misleading
as selecting
of an array
though
Although
of early
the
it was
rather
TO
it was certainly
idea of writing
C compilers offer “ Commercial checking that would help students otherwise extremely hard to find. messages
DECISION
to this
because
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3. THE
in C programs.
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presumably
programmers
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common sometimes
more
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highly wanted
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Many students contributed to become more involved.
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of that group
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how
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else,
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AN
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OVERVIEW
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significantly
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4.
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Strengthened
no matter
One
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gotten
in an introductory
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the project
that
legal
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. . . Thetis was a faithful mother to [Achilles], aiding him in all difficulties and watching over his interests from the first to the last.
Thetis
is a complete,
Hamilton,
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that “aids
students
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When
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reporting
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commercial
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302
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is consistent curve
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[Birch95].
of a program
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C environments
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and
to verify
EVALUATION
5.
By
restarting
notion
before
Montgomery,
Program
functions
repeatedly the
function
values.
code for running
Stanford
in Thet~:
input
reinforces
works
which
can
the IsPalindrome
without
a baffling
intended
a program
students errors
than they have been in the past.
the Macintosh
operation
where
click
is self-explanatory.
complicated
The debugger Stanford
sign
a simple
to be executed
the programmer
debugger
a stop
with
of these icons
of more
use, we find
after
margin
a breakpoint
to
accelerated
the material were
to
given from
CS 1
programming
the corresponding
questions
in
I
N=26 In general,
do yoLl jind
THINK
easv to use? Were you ever confused aboat how to do something
in THINK
Do you feel that THINK helped
you
Yes
I
collective
impression
lectures
are augmented
I 69.2%
C?
No 26.9%
I
73.170
C
that Thetis
~6,970
73.1%
C has
for students
ing ?
Do the error messages reported by THINK C help you find mistakes in your programs Despite
that
stronger
counterparts
in
those
contrast
Over helped
them
find
When
CS 106B
environments,
manv
users
mistakes,
students
said
while
fewer
than
execution
20
despite
students
who
switch
‘its
the choice
between
OUted to use Thetis
for their
slower
started
to THINK
&xecution
an assignment
C to take
speed. with
advantage
with
engineering.
portability
in mind
the immediate
indication and
programming the helper using
fewer
concentrate
Sahami,
students
spent
When
on it.
quarter
of 1995,
programs
were
significantly,
teaching less
assignments
students how
Thetis
than
during
Release
value allows
easily.
Gerald
section office
hours
Michael
Guide,
class
R.
the class they
Cambridge,
during
class,
checking
demonstrations
program
of the ACM,
D.
editing
education:
The results
al.,
in
March
“DYNALAB:
infrastructure
Bu[[etin,
A
featuring
March,
Corporation,
MA,
structure
[Roberts95a]
people allowed and bugs more
is also auDarent.
1995,
CodeCenter
User’s
1995. R.
on
Goldenstein,
“The
introductory
impact
computer
of
science
SIGCSE Bulletin,
so far,”
p~~grams
September
Mythology,Boston:
Eric
“Using
T/ze Art
S.
Roberts,
experience,” Martin C,”
MA:
courses: Ba[[etitl,
Ruckert Bulletin,
and
1993. of C: A
Addison-Wesley, Lilly,
as teaching
SIGCSE
S[GCSE
March
and Science
John
undergraduates
Little,
C in CS 1: Evaluating Bulletin,
Reading,
programming
“Educational
“Using
SIGCSE
S. Roberts,
[Roberts95b]
[Ruckert93]
Lecturers
Eric
Ai]proach,
Stanford
new
S. Roberts,
Librarv-Based 199.5.
introductory
supplementing
lecture notes with real programming examples. we have no direct evidence to support the
in-class
et
[Hamilton42] Edith Hamilton, Brown and Co., 1942.
the
but the better
sections.
of
1989.
on the average.
for presenting
and run-tilme
laboratory
SIGCSE
[Goldenstein89]
poll.”
the summer
and grade
formatting
the undergraduate
CenterLine
experience,”
tool
to
use
Birch,
science
Eric
to debug
enhancements
[Goldenstein89]
Cot]ltlllftzicatio?ls
[Roberts93]
or discussion
for demonstrations
for
science,”
the Stanford
staff
of
slower
Austing, Bruce Barnes, Della and Gordon Stokes, “Curriculum
Recommendations
each
to the course leaders
Richard Engel,
more
usual,
its
REFERENCES
to finish
than
by
platforms
Perhaps
hours
these
advantage
help system
for general
usual.
It is also an excellent
during
use Thetis
of Thetis
to other
the system
Rollins,
The
topics
Port Thetis
●
animation,”
quickly,
more
●
on-line
required
support from the programming environment to move beyond simple misunderstandings
Thetis
to support
[CenterLine95]
thought
by the
believe
1979.
to program
generally
at
times
needed
automat]c
the visualizer
[Birch95]
and
time
to
released five
We
editors
Enhance
program
much
to provide
●
to step over
he asks
and how
of time
no easier
the following
stylistic,
hurdles
a “pain
by one or two
were
to make
an effective
computer
evaluates
that people
painful
frustrated
in structure-based
dynamic
at Stanford,
with
becoming
more syntactic,
’78:
common
by conducting
be
to take full
Develop
computer
or accessing
and painful
it was
he noted
dropped
allows
at
Students
find
students
the text editor
Bonnette,
own and therefore
in an assignment,
painful
the amount
assignment The
a lecturer
hand
how
their
goal of learning
on assignments
collectively
to
paper.
been
utilization.
over the next two years:
[Austing79]
introductory
a variable
confusing
on the main
performance When
Thetis
often
reduced
cluster.
will
the memory
in this
allow
memory
which
less than half
will
important
have
runs approximately
Provide
to fit
asked by students
able
initializing
array element-on
yet
taking
computing
generally
as not questions.
Mehran
tools
Thetis,
of 1995,
●
to program
has successfully
are the questions
were
an out-of-bounds small,
how
development
in several
challenges
●
run
of their lesson in
to choose
of students
in the main
of
without
Extend
7.
that Thetis
classes cubicle
Thetis
these
and also how
frustration
mistakes—such asked
learned
Thetis
our
and reduce
discussed
the sort found
task at hand.
Another the stress
Students
version
and requires
Thetis
would
faster
and
environment
performance.
Often,
Thetis
of the
times when they were doing the final fine-tuning programs. This practice constituted a valuable software
efficiency
We also intend
given
we believe
learning
the system
technical
in the fall
Thetis
●
programs
next
improvements
the error
better
continuing
primary
implementation
of error
PLANS
in the last year,
we set out to accomplish
to improve
increase
faster
The
however,
Our
Stanford
when
in CS 1/CS2.
are,
and expect
The
trouble
the goals
in better
in Thetis.
FUTURE
a significantly
ways.
C.
were
students
more
a
their
in CSI 06A.
the usefulness
of Thetis
said the same of THINK
y have than
having
Thetis
concerns
80 percent
typical]
computing
using
significant
messages
in CS 106X
they reported
most
percent
students
background C than
THINK
messages.
work
in CS 106A,
using
We
80.8%
19.2%
easilv ?
the fact
much
fulfills
that it provides
understand
]rogramm
AND
On the basis of our experien~e
I
1
ideas sink
by demonstrations
CONCLUSIONS
6.
30.8%
is that new
An
and
update
March
on
Halpern,
1993.
[Schorsch95] Tom Schorsch, “CAP: An automated assessment tool to check Pascal programs for syntax,
Although claim, our
and style
304
errors,”
SIGCSE
Bulletinj
March
in the
1995.
Richard
March
Bryan
assistants
1995.
selflogic.
