ch06 arrays and vectors - 國立臺灣大學ccf.ee.ntu.edu.tw/~ypchiou/cpp_programming/ch06...
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Ph
oto
nic
Mo
de
ling
an
d D
es
ign
La
b.
Gra
du
ate
Ins
titute
of P
ho
ton
ics
an
d O
pto
ele
ctro
nic
s &
De
pa
rtme
nt o
f Ele
ctric
al E
ng
ine
erin
g
Na
tion
al T
aiw
an
Un
ive
rsity
C++C++C++C++Programming
ProgrammingProgrammingProgrammingChapter 6
Arrays and VectorsYihYihYih Yih--- -Peng
PengPengPengChiou
ChiouChiouChiou
Room 617, BL BuildingRoom 617, BL BuildingRoom 617, BL BuildingRoom 617, BL Building
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360336033603
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2
ObjectivesObjectivesObjectivesObjectives
�T
his ch
apter in
trod
uces th
e imp
ortan
t top
ic of d
ata structu
res—co
llections
of related
data item
s.
�A
rrays
are data stru
ctures co
nsistin
g o
f related d
ata items o
f the sam
ety
pe.
�A
fter discu
ssing h
ow
arrays are d
eclared, created
and
initialized
, we
presen
t a series of p
ractical exam
ples th
at dem
on
strate several co
mm
on
array m
anip
ulatio
ns.
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ContentsContentsContentsContents
3
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�A
con
secutiv
e gro
up
of m
emo
ry lo
cation
s that all h
ave th
e same ty
pe.
�T
o refer to
a particu
lar locatio
n o
r elemen
t in th
e array�
specify
the n
ame
of th
e array an
d th
e po
sition n
um
ber
of th
e elemen
t�
an in
teger array
called c
.
�12 elem
ents.
4
6.2
Arra
ys
�P
ositio
n n
um
ber, fo
rmally
called
a subscrip
tor in
dex
(this n
um
ber sp
ecifies the
num
ber o
f elemen
ts from
the
beg
innin
g o
f the array
).
�1
stelemen
t in ev
ery array
has su
bscrip
t 0 (zero
), and is
som
etimes called
the zero
thelem
ent .
�H
ighest su
bscrip
t in array
cis 1
1 (=
12-1
)
�A
void
off-b
y-o
ne e
rror
�S
pecify
an elem
ent ex
plicitly
�A
subscrip
t must b
e an
integ
er or in
teger ex
pressio
n
(usin
g an
y in
tegral ty
pe).
, e.g., c
[6]
c[6]
c[6]
c[6], c[7]
c[7]
c[7]
c[7]
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6.2
Arra
ys
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�A
rrays o
ccup
y sp
ace in m
emo
ry.
�D
eclaration
form
:
�typearrayName[ arraySize];
�T
he co
mp
iler reserves th
e app
rop
riate amo
un
t of m
emo
ry.
�A
rrays can
be d
eclared to
con
tain v
alues o
f any
non
reference
data ty
pe.
6
6.3
De
cla
ring
Arra
ys
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�Initializing an array’s elements to zeros andprinting the array
7
6.4
Ex
am
ple
s U
sin
g A
rray 6.4.1
6.4.16.4.16.4.1Declaring an
Declaring an Declaring an Declaring an
Array and Using a Loop to Initialize the Array’s ElementsArray and Using a Loop to Initialize the Array’s ElementsArray and Using a Loop to Initialize the Array’s ElementsArray and Using a Loop to Initialize the Array’s Elements
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�If th
ere are fewer in
itializers than
elemen
ts in th
e array, th
e remain
ing
array
elemen
ts are initialized
to zero
. (mo
re =>
com
pilatio
n erro
r)
8
6.4
Exam
ple
s U
sin
g A
rray
6.4
.2Initializing an Array in a Declaration with an Initializer List
�If th
e array size is o
mitted
from
a declaratio
n w
ith
an in
itializer list, the co
mp
iler determ
ines th
e n
um
ber o
f elemen
ts in th
e array b
y co
un
ting th
e n
um
ber o
f elemen
ts in th
e initializer list.
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�The size of automatic
automaticautomaticautomaticand static
staticstaticstaticarrays should
be a constant. (dynamicdynamicdynamicdynamic=> variable OK)
9
6.4.36.4.36.4.36.4.3Specifying an Array’s Size with a Constant Variable
Specifying an Array’s Size with a Constant Variable Specifying an Array’s Size with a Constant Variable Specifying an Array’s Size with a Constant Variable and Setting Array Elements with Calculationsand Setting Array Elements with Calculationsand Setting Array Elements with Calculationsand Setting Array Elements with Calculations
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�L
ine 1
0 u
ses the c
onst
qu
alifierto
declare a so
-called co
nstan
t
variab
learraySize
with
the v
alue 1
0.
�C
on
stant v
ariables m
ust b
e initialized
with
a con
stant ex
pressio
n
wh
en th
ey’re d
eclared an
d can
no
t be m
od
ified th
ereafter.
�C
on
stant v
ariables are also
called n
amed
con
stants
or read
-on
ly
variab
les.
10
6.4.36.4.36.4.36.4.3Specifying an Array’s Size with a Constant Variable
Specifying an Array’s Size with a Constant Variable Specifying an Array’s Size with a Constant Variable Specifying an Array’s Size with a Constant Variable and Setting Array Elements with Calculationsand Setting Array Elements with Calculationsand Setting Array Elements with Calculationsand Setting Array Elements with Calculations
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6.4.36.4.36.4.36.4.3Specifying an Array’s Size with a Constant Variable
Specifying an Array’s Size with a Constant Variable Specifying an Array’s Size with a Constant Variable Specifying an Array’s Size with a Constant Variable and Setting Array Elements with Calculationsand Setting Array Elements with Calculationsand Setting Array Elements with Calculationsand Setting Array Elements with Calculations
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6.4
.4Summing the Elements of an Array
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6.4
.5Using Bar Charts to Display Array Data
Graphically
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6.4
.5Using Bar Charts to Display Array Data Graphically
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6.4
.6Using the Elements of an Array as Counters
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�U
ses arrays to
sum
marize th
e results o
f data co
llected in
a surv
ey.
�F
orty
stud
ents w
ere asked
to rate th
e qu
ality o
f the fo
od
in th
e stud
ent
cafeteria on
a scale of 1
to 1
0 (1
mean
ing
awfu
l and
10
mean
ing
ex
cellent). P
lace the 4
0 resp
on
ses in an
integ
er array an
d su
mm
arize th
e results o
f the p
oll.
�C
++
has n
o a
rray
bo
un
ds ch
eckin
g to
prev
ent th
e com
pu
ter from
referrin
g to
an elem
ent th
at do
es no
t exist.
�T
hu
s, an ex
ecutin
g p
rog
ram can
“walk
off” eith
er end
of an
array
with
ou
t warn
ing
.
�Y
ou
sho
uld
ensu
re that all array
references rem
ain w
ithin
the b
ou
nd
s of
the array
.
17
6.4
.7Using Arrays to Summarize Survey Results
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6.4
.7Using Arrays to Summarize Survey Results
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6.4
.7Using Arrays to Summarize Survey Results
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6.4
.7Using Arrays to Summarize Survey Results
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�A
pro
gram
initializes s
tatic
local array
s wh
en th
eir declaratio
ns
are first enco
un
tered.
�If a s
tatic
array is n
ot in
itialized ex
plicitly
by
yo
u, each
elemen
t
of th
at array is in
itialized to
zero b
y th
e com
piler w
hen
the array
is
created.
21
6.4
.8Static Local Arrays and Automatic Local Arrays
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6.4
.8Static Local Arrays and Automatic Local Arrays
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6.4
.8Static Local Arrays and Automatic Local Arrays
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6.4
.8Static Local Arrays and Automatic Local Arrays
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6.4
.8Static Local Arrays and Automatic Local Arrays
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�T
o p
ass an array
argu
men
t to a fu
nctio
n, sp
ecify th
e nam
e of th
e array
with
ou
t any
brack
ets.�
the array
size is no
rmally
passed
as well
�C
++
passes array
s to fu
nctio
ns b
yreferen
ce�
the called
fun
ction
s can m
od
ify th
e elemen
t in th
e callers’ orig
inal array
s.
�T
he v
alue o
f the n
ame o
f the array
is the ad
dress
in th
e com
pu
ter’s m
emo
ry o
f the first elem
ent o
f the array
.�
the called
fun
ction
kn
ow
s precisely
wh
ere the array
is stored
in m
emo
ry
�In
div
idu
al array elem
ents are p
assed b
y v
alue ex
actly as sim
ple v
ariable
�S
uch
simp
le sing
le pieces o
f data are called
scalarso
r scalar qu
antities.
26
6.5
Pa
ss
ing
Arra
ys
to F
un
ctio
ns
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6.5
Pa
ss
ing
Arra
ys
to F
un
ctio
ns
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6.5
Pa
ss
ing
Arra
ys
to F
un
ctio
ns
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6.5
Pa
ss
ing
Arra
ys
to F
un
ctio
ns
(By
structu
re or class)
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6.6
Se
arc
hin
g A
rray
s w
ith L
ine
ar S
ea
rch
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�S
earchin
g: d
etermin
e wh
ether an
array o
f totally
Nelem
ents co
ntain
s
a valu
e that m
atches a certain
key
valu
e.
�L
inear search
com
pares each
elemen
t of an
array w
ith a search
key
�N
o p
articular o
rder: fo
un
d in
the 1
st elemen
t as the last.
�O
n av
erage, co
mp
are the search
key
with
N/2
elemen
ts
33
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�S
ortin
g d
ata
(排序
) -p
lacing
the d
ata into
som
e particu
lar ord
er,
e.g. ascen
din
g o
r descen
din
g
�an
intrig
uin
g p
rob
lem th
at has attracted
som
e of th
e mo
st inten
se
research effo
rts in th
e field o
f com
pu
ter science.
�In
sertion
sort —
a simp
le, bu
t inefficien
t, sortin
g alg
orith
m.
�In
serti-th
elemen
etin
to (i-1
) sorted
elemen
ts to m
ake i
sorted
elem
ents.
�i=
1, n
o so
rting i=
2, i=
3, …
34
6.7
So
rting
Arra
ys
with
Ins
ertio
n S
ort
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�A
rrays w
ith tw
o d
imen
sion
s (i.e., sub
scripts) o
ften rep
resent tab
les o
f valu
es con
sisting
of in
form
ation
arrang
ed in
row
san
d co
lum
ns.
�T
o id
entify
a particu
lar table elem
ent w
ith tw
o su
bscrip
ts.
�B
y co
nv
entio
n, th
e 1st=
> ro
w th
e 2n
d=
> co
lum
n.
�O
ften called
two
-dim
ensio
nal array
so
r 2-D
arrays.
�A
rrays w
ith tw
o o
r mo
re dim
ensio
ns are k
no
wn
as mu
ltidim
ensio
nal
arrays.
37
6.8
Mu
ltidim
en
sio
na
l Arra
ys
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�C
an b
e initialized
in d
eclaration
, valu
es gro
up
ed b
y ro
w in
braces
�If n
ot en
ou
gh
initializers fo
r a giv
en ro
w, rem
ainin
g elem
ents o
f that
row
are initialized
to 0
.
38
6.8
Mu
ltidim
en
sio
na
l Arra
ys
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6.9
Case S
tud
y: P
rocessin
g G
rad
es in
a
Tw
o-D
imen
sio
nal A
rray
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�vector
: a mo
re rob
ust ty
pe o
f array featu
ring
man
y ad
ditio
nal cap
abilities
�C
-style p
oin
ter-based
arrays: p
oten
tial for erro
rs and
are no
t flexib
le
�can
easily “w
alk o
ff” either en
d o
f an array
, becau
se C+
+ d
oes n
ot ch
eck
�T
wo
arrays can
no
t be m
eanin
gfu
lly co
mp
ared w
ith relatio
nal o
perato
rs
�W
hen
an array
is passed
to a g
eneral-p
urp
ose fu
nctio
n d
esign
ed to
han
dle
arrays o
f any size, its size m
ust b
e passed
as an ad
ditio
nal arg
um
ent.
�O
ne array
cann
ot b
e assign
ed to
ano
ther w
ith th
e assign
men
t op
erator(s).
�C
lass temp
late vector
allow
s yo
u to
create a mo
re po
werfu
l and
less erro
r-pro
ne altern
ative to
arrays.
�S
tand
ard class tem
plate v
ector
is defin
ed in
head
er <vector>
and
belo
ng
s to
nam
espace s
td
46
6.1
0In
trod
uctio
n to
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+ S
tan
dard
Lib
rary
Cla
ss
Tem
pla
te vector
vector
vector
vector
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47
YP
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EIn
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48
YP
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EIn
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49
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50
YP
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51
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�B
y d
efault, all th
e elemen
ts of a v
ector
ob
ject are set to 0
.
�vector
s can b
e defin
ed to
store an
y d
ata typ
e.
�vector
mem
ber fu
nctio
n size
ob
tain th
e nu
mb
er of elem
ents.
�U
can u
se squ
are brack
ets, []
, to access th
e elemen
ts in a v
ector
.
�vector
ob
jects can b
e com
pared
with
on
e ano
ther u
sing
the
equ
ality o
perato
rs.
�Y
ou
can create a n
ew vector
ob
ject that is in
itialized w
ith a co
py
o
f an ex
isting
vector
.
�Y
ou
can u
se the assig
nm
ent (=
) op
erator w
ith vector
ob
jects.
�A
s with
C-sty
le po
inter-b
ased array
s, C+
+ d
oes n
ot p
erform
any
bo
un
ds ch
eckin
g w
hen
vector
elemen
ts are accessed w
ith sq
uare
brack
ets.
�S
tand
ard class tem
plate v
ector
pro
vid
es bo
un
ds ch
eckin
g in
its
mem
ber fu
nctio
n at
, wh
ich “th
row
s an ex
ceptio
n” (see C
hap
ter1
6,
Ex
ceptio
n H
and
ling
) if its argu
men
t is an in
valid
sub
script.
52
6.1
0In
trod
uctio
n to
C+
+ S
tan
dard
Lib
rary
Cla
ss
Tem
pla
te vector
vector
vector
vector
YP
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53
6.1
1In
trod
uctio
n to
C+
+ S
tan
dard
Lib
rary
Cla
ss
string
string
string
string
YP
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NT
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& E
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54
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55
YP
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56
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�L
ine 1
6 read
s the lin
e of tex
t from
the u
ser by
usin
g th
e library
fun
ction
getline
(from
the h
eader file <
string>
).
�We can’t simply write �
cin>> s4; to
ob
tain a lin
e of tex
t.
�W
hen
cinis u
sed w
ith th
e stream ex
traction
op
erator, it read
s
characters u
ntil th
e first wh
ite-space ch
aracter is reached
.
�L
ines 2
7–
33
sho
w th
e results o
f com
parin
g strin
gs b
y u
sing
class
string
’s ov
erload
ed eq
uality
and
relation
al op
erators.
�T
hese o
perato
rs perfo
rm lex
icog
raph
ical com
pariso
ns o
n strin
g
ob
jects—th
ey co
mp
are the n
um
erical valu
es of th
e characters
(see Ap
pen
dix
B, A
SC
II Ch
aracter Set) in
each strin
g.
�C
lass string
pro
vid
es mem
ber fu
nctio
n em
pty
, wh
ich retu
rns tru
e if
the strin
g is em
pty
; oth
erwise, it retu
rns false.
57
6.1
1In
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uctio
n to
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tan
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Lib
rary
Cla
ss
string
string
string
string
YP
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�L
ine 4
1 d
emo
nstrates class x
’s ov
erload
ed assig
nm
ent o
perato
r.
�L
ine 4
7 d
emo
nstrates class strin
g’s o
verlo
aded
+=o
perato
r for
string
con
catenatio
n.
�L
ine 5
2 d
emo
nstrates th
at a string
literal can also
be ap
pen
ded
to
a string
ob
ject by
usin
g o
perato
r +=.
�C
lass string
pro
vid
es mem
ber fu
nctio
n substr
(lines 5
8 an
d 6
3) to
return
a po
rtion
of a strin
g as a strin
g o
bject.
�T
he v
ersion
with
two
argu
men
ts ob
tains th
e nu
mb
er of
characters sp
ecified b
y th
e secon
d arg
um
ent startin
g at th
e
po
sition
specified
by
the first arg
um
ent.
�T
he sin
gle arg
um
ent v
ersion
ob
tains a su
bstrin
g startin
g fro
m th
e
specified
ind
ex.
�C
lass string
’s ov
erload
ed []
op
erator can
be u
sed to
create lvalu
es
that en
able n
ew ch
aracters to rep
lace existin
g ch
aracters in a strin
g.
�N
o b
ou
nd
s check
ing
is perfo
rmed
.
58
6.1
1In
trod
uctio
n to
C+
+ S
tan
dard
Lib
rary
Cla
ss
string
string
string
string
YP
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rog
ram
min
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TU
BA
�C
lassstring’s o
verlo
aded
[]
op
erator can
be u
sed to
ob
tain th
e
character at a sp
ecified in
dex
.
�C
lassstring
pro
vid
es bo
un
ds ch
eckin
g in
its mem
ber fu
nctio
n
at, w
hich
thro
ws an
excep
tion
if its argu
men
t is an in
valid
sub
script.
�Erase a vector : http://www.cplusplus.com/reference/stl/vector/erase/
�Two and multi-dimensional vectors
59
6.1
1In
trod
uctio
n to
C+
+ S
tan
dard
Lib
rary
Cla
ss
string
string
string
string