Cao Tun Dng dungct@soict.hut.edu.vn

Bi 02. C php Java/C++ c bn

LP TRNH HNG I TNG

B mn Cng ngh phn mm VIN CNG NGH THNG TIN TRUYN THNG

TRNG I HC BCH KHOA H NI

Mc tiu bi hc

Nu c cc quy c t tn trong cc chng trnh Java/C++

To ra cc nh iu kin, cu trc lp v r nhnh hp l

M t cc kiu d liu c bn trong Java v cch s dng

Cc ton t S dng cc cu lnh Gii thch v phm vi ca bin Khai bo, khi to cc bin v mng trong Java

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Ni dung

1. nh danh

2. Cc kiu d liu

3. Ton t

4. Cu trc iu khin

5. Mng

3

Ni dung

1. nh danh

2. Cc kiu d liu

3. Ton t

4. Cu trc iu khin

5. Mng

4

1. nh danh

nh danh: Xu k t th hin tn cc bin, cc

phng thc, cc lp v nhn

Quy nh vi nh danh: Cc k t c th l ch s, ch ci, '$'

hoc _ Tn khng c php:

Bt u bi mt ch s Trng vi t kha

Phn bit ch hoa ch thng Yourname, yourname, YourName v

yourName l 4 nh danh khc nhau

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1. nh danh (2)

Quy c vi nh danh (naming convention): Bt u bng ch ci Gi (package): tt c s dng ch thng

theexample

Lp (Class): vit hoa ch ci u tin trong cc t ghp li TheExample

Phng thc/thuc tnh (method/field): Bt u bng ch thng, vit hoa ch ci u tin trong cc t cn li theExample

Hng (constants): Tt c vit hoa THE_EXAMPLE

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1. nh danh (3)

Literals null true false

T kha (keyword) abstract assert boolean break byte case catch char class continue default do double else

extends final finally float for if implements

import instanceof int interface long native new

package private protected public return short

static strictfp super switch synchronized this

throw throws transient try void volatile while

T dnh ring (reserved for future use) byvalue cast const future generic goto inner operator outer rest var volatile

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Ni dung

1. nh danh

2. Cc kiu d liu

3. Ton t

4. Cu trc iu khin

5. Mng

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2. Cc kiu d liu

Trong Java kiu d liu c chia thnh hai loi: Kiu d liu nguyn thy (primitive)

S nguyn (integer) S thc (float) K t (char) Gi tr logic (boolean)

Kiu d liu tham chiu (reference) Mng (array) i tng (object)

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2.1. Kiu d liu nguyn thy

Mi bin u phi khai bo mt kiu d liu

Cc kiu d liu c bn cha mt gi tr n

Kch thc v nh dng phi ph hp vi kiu ca n

Java phn loi thnh 4 kiu d liu nguyn thy

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a. S nguyn

S nguyn c du

Khi to vi gi tr 0

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b. S thc

Khi to vi gi tr 0.0

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c. K t

K t Unicode khng du, c t gia hai du nhy n

2 cch gn gi tr: S dng cc ch s trong h 16: char uni ='\u05D0';

S dng k t: char a = A;

Gi tr mc nh l gi tr zero (\u0000)

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d. Gi tr logic Gi tr boolean c xc nh r rng trong Java

Mt gi tr int khng th s dng thay cho gi tr boolean

C th lu tr gi tr hoc true hoc false

Bin boolean c khi to l false

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2.2. Gi tr hng (literal)

Literal l mt gi tr ca cc kiu d liu nguyn thy v xu k t.

Gm 5 loi: integer

floating point

boolean

character

string

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Literals

integer..7 floating point7.0f boolean.true character.'A' string.."A"

a. S nguyn

H c s 8 (Octals) bt u vi ch s 0 032 = 011 010(2) = 16 + 8 + 2 = 26(10)

H c s 16 (Hexadecimals) bt u vi 0 v k t x 0x1A = 0001 1010(2) = 16 + 8 + 2 = 26(10)

Kt thc bi k t L th hin kiu d liu long 26L

K t hoa, thng cho gi tr bng nhau 0x1a , 0x1A , 0X1a , 0X1A u c gi tr 26 trong h

decimal

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b. S thc

float kt thc bng k t f (hoc F) 7.1f

double kt thc bng k t d (hoc D) 7.1D

e (hoc E) c s dng trong dng biu din

khoa hc: 7.1e2

Mt gi tr thc m khng c k t kt thc i km s c kiu l double 7.1 ging nh 7.1d

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c. boolean, k t v xu k t

boolean: true False

K t: c t gia 2 du nhy n

V d: a, A hoc '\uffff

Xu k t: c t gia hai du nhy kp V d: Hello world, Xin chao ban,

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d. Escape sequence

Cc k t iu khin nhn phm \b backspace \f form feed \n newline \r return (v u dng) \t tab

Hin th cc k t c bit trong xu \" quotation mark \ apostrophe \\ backslash

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2.3. Chuyn i kiu d liu (Casting)

Java l ngn ng nh kiu cht Gn sai kiu gi tr cho mt bin c th dn n cc

li bin dch hoc cc ngoi l ca JVM

JVM c th ngm nh chuyn t mt kiu d liu hp sang mt kiu rng hn

chuyn sang mt kiu d liu hp hn, cn phi nh kiu r rng.

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int a, b;

short c;

a = b + c;

int d;

short e;

e = (short)d;

double f;

long g;

f = g;

g = f; //error

2.3. Chuyn i kiu d liu (2)

Chuyn i kiu s c thc hin t ng nu khng xy ra mt mt thng tin byte short int

long float double p kiu trc tip

(explicit cast) c yu cu nu c nguy c gim chnh xc

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V d - chuyn i kiu

long p = (long) 12345.56; // p == 12345

int g = p; // khng hp l d kiu int

//c th lu gi tr 12345

char c = t;

int j = c; // t ng chuyn i

short k = c; // khng hp l

short k = (short) c; // p kiu trc tip

float f = 12.35; // khng hp l

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2.4. Khai bo v khi to bin

Cc bin n (bin khng phi l mng) cn phi c khi to trc khi s dng trong cc biu thc C th kt hp khai bo v khi to cng mt lc. S dng = gn (bao gm c khi to)

V d: int i, j; // Khai bo bin i = 0; int k =i+1; float x=1.0f, y=2.0f; System.out.println(i); // In ra 0 System.out.println(k); // In ra 1 System.out.println(j); // Li bin dch

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Ch thch

Java h tr ba kiu ch thch nh sau: // Ch thch trn mt dng

// Khng xung dng

/* Ch thch mt on */

/** Javadoc * ch thch dng Javadoc */

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Cu lnh

Cc cu lnh kt thc bi du;

Nhiu lnh c th vit trn mt dng

Mt cu lnh c th vit trn nhu dng V d:

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System.out.println(

This is part of the same line);

a=0; b=1; c=2;

Ni dung

1. nh danh

2. Cc kiu d liu

3. Ton t

4. Cu trc iu khin

5. Mng

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3. Ton t (Operators)

Kt hp cc gi tr n hoc cc biu thc con thnh nhng biu thc mi, phc tp hn v c th tr v gi tr.

Java cung cp nhiu dng ton t sau:

Ton t s hc

Ton t bit, ton t quan h

Ton t logic

Ton t gn

Ton t mt ngi

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3. Ton t (2)

Ton t s hc +, -, *, /, %

Ton t bit AND: &, OR: |, XOR: ^, NOT: ~

Dch bit:

Ton t quan h ==, !=, >, =,

3. Ton t (3)

Ton t mt ngi o du: +, -

Tng gim 1 n v: ++, --

Ph nh mt biu thc logic: !

Ton t gn =, +=, -=, %= tng t vi >>,

Th t u tin ca ton t

Cho bit ton t no thc hin trc c xc nh bi cc du ngoc n hoc theo ngm nh nh sau: Postfix operators [] . (params) x++ x-- Unary operators ++x --x +x -x ~ ! Creation or cast new (type)x Multiplicative * / % Additive + - Shift > >>> (unsigned shift) Relational < > = instanceof Equality == != Bitwise AND & Bitwise exclusive OR ^ Bitwise inclusive OR | Logical AND && Logical OR || Conditional (ternary) ?: Assignment = *= /= %= += -= >>= >= &= ^= |=

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Ni dung

1. nh danh

2. Cc kiu d liu

3. Ton t

4. Cu trc iu khin

5. Mng

32

4.1. Lnh if - else

C php if (dieu_kien){

cac_cau_lenh;

}

else {

cac_cau_lenh;

}

Biu thc iu kin nhn gi tr boolean

Mnh else l ty chn

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V d - Kim tra s chn l

class CheckNumber

{

public static void main(String args[])

{

int num =10;

if (num %2 == 0)

System.out.println (num+ la so chan);

else

System.out.println (num + la so le);

}

}

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C++: Gii phng trnh bc nht #include

int main(){

float a, b;

cout a;

cout

4.2. Lnh switch - case

Kim tra mt bin n vi nhiu gi tr khc nhau v thc hin trng hp tng ng

break: Thot khi lnh switch-case

default kim sot cc gi tr nm ngoi cc gi tr case:

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case a action(s)

break

default action(s)

[true]

case b action(s)

break

case z action(s)

break

.

.

.

[false] case a

[true]

[true]

case b

case z

[false]

[false]

V d - Lnh switch - case

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if (day == 0 || day == 1) {

rule = weekend;

} else if (day > 1 && day

4.3. Vng lp while v do while

Thc hin mt cu lnh hoc mt khi lnh khi iu kin vn nhn gi tr true while() thc hin 0 hoc nhiu ln

do...while() thc hin t nht mt ln

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int x = 2;

while (x < 2) {

x++;

System.out.println(x);

} int x = 2;

do {

x++;

System.out.println(x);

} while (x < 2);

action state

[true]

[false]

condition

V d - Vng lp while

class WhileDemo{

public static void main(String args[]){

int a = 5,fact = 1;

while (a >= 1){

fact *=a;

a--;

}

System.out.println(The Factorial of 5

is +fact);

}

}

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4.4. Vng lp for C php: for (start_expr; test_expr; increment_expr){

// code to execute repeatedly

}

3 biu thc u c th vng mt

C th khai bo bin trong cu lnh for Thng s dng khai bo mt bin m

Thng khai bo trong biu thc start

Phm vi ca bin gii hn trong vng lp

V d: for (int index = 0; index < 10; index++) {

System.out.println(index);

}

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V d - vng lp for

class ForDemo

{

public static void main(String args[])

{

int i=1, sum=0;

for (i=1;i

4.5. Cc lnh thay i cu trc iu khin

break C th c s dng thot ra ngoi cu lnh

switch

Kt thc vng lp for, while hoc do...while

C hai dng: Gn nhn: Tip tc thc hin cu lnh tip theo sau

vng lp c gn nhn

Khng gn nhn: Thc hin cu lnh tip theo bn ngoi vng lp

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4.5. Cc lnh thay i cu trc iu khin (2)

continue C th c s dng cho vng lp for, while hoc

do...while

B qua cc cu lnh cn li ca vng lp hin thi v chuyn sang thc hin vng lp tip theo.

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V d - break v continue

public int myMethod(int x) {

int sum = 0;

outer: for (int i=0; i

4.6. Phm vi bin

Phm vi ca bin l vng chng trnh m trong bin c th c tham chiu n

Cc bin c khai bo trong mt phng thc th ch c th truy cp trong phng thc

Cc bin c khai bo trong vng lp hoc khi lnh th ch c th truy cp trong vng lp hoc khi lnh

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Phm vi hot ng ca cc bin

Phm vi hot ng (scope) ca cc bin cho php xc nh cc nguyn l ca to bin, s dng bin v gii phng bin

C++ cho php nh ngha cc bin ti mi im trong chng trnh (on the fly)

Phn loi: bin ton cc (global), bin cc b, bin static

Java: t kha static cho phm vi ton cc

Ton t phm vi :: (C++)

Gip phn bit bin cc b v bin ton cc cng tn. #include

int counter = 50; // global variable

int main() {

for (register int counter = 1; // this refers to the counter < 10; // local variable

counter++){

printf("%d\n", ::counter // global variable

/ // divided by

counter); // local variable

}

return 0;

}

Trong Java khng tn ti khi nim ton t phm vi

Ni dung

1. nh danh

2. Cc kiu d liu

3. Ton t

4. Cu trc iu khin

5. Mng

49

5. Mng (array)

Tp hp hu hn cc phn t cng kiu

Phi c khai bo trc khi s dng

Khai bo: C php:

kieu_dlieu[] ten_mang = new kieu_dlieu[KT_MANG];

kieu_dlieu ten_mang[] = new kieu_dlieu[KT_MANG];

V d: char c[] = new char[12];

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reference

Array or Object

variableName

5.1. Khai bo v khi to mng

Khai bo, khi to gi tr ban u: C php:

kieu_dl[] ten_mang = {ds_gia_tri_cac_ptu};

V d: int[] number = {10, 9, 8, 7, 6};

Nu khng khi to nhn gi tr mc nh ty thuc vo kiu d liu.

Lun bt u t phn t c ch s 0

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Tn ca mng (tt c cc thnh phn trong mng c cng tn, c)

Ch s (truy nhp n cc thnh phn ca mng thng qua ch s)

c[ 0 ]

c[ 1 ]

c[ 2 ]

c[ 3 ]

c[ 4 ]

c[ 5 ]

c[ 6 ]

c[ 7 ]

c[ 8 ]

c[ 9 ]

c[ 10 ]

c[ 11 ]

-45

6

0

72

1543

-89

0

62

-3

1

6453

78

c.length: cho bit di ca mng c

V d - mng

5.1. Khai bo v khi to mng (2)

V d: int MAX = 5;

boolean bit[] = new boolean[MAX];

float[] value = new float[2*3];

int[] number = {10, 9, 8, 7, 6};

System.out.println(bit[0]); // prints false

System.out.println(value[3]); // prints 0.0

System.out.println(number[1]); // prints 9

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5.2. Mng nhiu chiu

Bng vi cc dng v ct Thng s dng mng hai chiu

V d khai bo mng hai chiu b[2][2]

int b[][] = { { 1, 2 }, { 3, 4 } }; 1 v 2 c khi to cho b[0][0] v b[0][1]

3 v 4 c khi to cho b[1][0] v b[1][1]

int b[3][4];

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5.2. Mng nhiu chiu (2)

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b[ 1 ][ 0 ] b[ 1 ][ 1 ] b[ 1 ][ 2 ] b[ 1 ][ 3 ]

Row 0

Row 1

Row 2

Column 0 Column 1 Column 2 Column 3

Ch s hng

Tn mng

Ch s ct

b[ 0 ][ 0 ] b[ 0 ][ 1 ] b[ 0 ][ 2 ] b[ 0 ][ 3 ]

b[ 2 ][ 0 ] b[ 2 ][ 1 ] b[ 2 ][ 2 ] b[ 2 ][ 3 ]

C++: Cp pht b nh ng Ton t cp pht b nh ng new. C hai

cch s dng new: Cp pht b nh cho mt bin

new type;

gi tr tr v l: mt con tr ch n v tr tng ng khi cp

pht thnh cng v NULL trong trng hp tri li.

Cp pht mt mng ng cc phn t new type[n]

gi tr tr v l:

Con tr ch n u vng nh cha n phn t thuc kiu type

NULL khi khng cn b nh cp pht

C++: thu hi b nh ng

Ton t gii phng vng nh ng (heap) delete

delete con_tr;

delete [] con_tr;

Tr li vng nh tr bi con_tr

Sau lnh delete gi tr ca con_tr

khng xc nh

C++: new v delete

V d: Vi khai bo int *adr;

lnh adr=new int; s cp pht mt vng nh cn thit cho mt

gi tr kiu int v gn a ch cho adr. lnh: delete adr; s gii phng vng nh tr bi adr;

Lnh char *adc= new char[100];

s cp pht mt vng nh cha 100 k t v t a ch u vng nh vo bin adc.

Lnh delete adc; s gii phng vng nh ny.

R r b nh

Vn : mt mi con tr n mt vng b nh c cp pht. Khi , vng b nh bmt du, khng th tr li cho heap c.

int* ptr = new int; *ptr = 8; int* ptr2 = new int; *ptr2 = -5; ptr = ptr2;

8

ptr

-5

ptr2

8

ptr

-5

ptr2

Con tr lc

Khi delete ptr2, ta cn ch khng xo vng b nh m mt con tr ptr khc ang tr ti.

int* ptr = new int; *ptr = 8; int* ptr2 = new int; *ptr2 = -5; ptr = ptr2; delete ptr2; // ptr is left

dangling ptr2 = NULL;

8

ptr

-5

ptr2

8

ptr

NULL

ptr2