Moät soá kieán thöùc cô sôû veà laäp trình baèng ngoân ngöõ C

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IV. Kieåu vaø teân döõ lieäu trong C

Noäi dung:

Vôùi phaàn naøy ta laøm quen vôùi caùc boán kieåu döõ lieäu cô sôû cuûa ngoân ngöõ C:

• char
• int
• float
• double

Töø khoùa

Töø khoùa laø töø daønh rieâng ñeå xaùc ñònh moät ñaëc tröng cuûa ngoân ngöõ, khoâng ñöôïc duøng laøm bieán, haèng hoaëc teân haøm. ANSI C coù 32 töø khoùa sau (vaø chæ vieát baèng chöõ thöôøng !!):

Keyword	Description	Keyword	Description
auto	Storage class specifier	int	Type specifier
break	Statement	long	Type specifier
case	Statement	register	Storage class specifier
char	Type specifier	return	Statement
const	Storage class modifier	short	Type specifier
continue	Statement	signed	Type specifier
default	Label	sizeof	Operator
do	Statement	static	Storage class specifier
double	Type specifier	struct	Type specifier
else	Statement	switch	Statement
enum	Type specifier	typedef	Statement
extern	Storage class specifier	union	Type specifier
float	Type specifier	unsigned	Type specifier
for	Statement	void	Type specifier
goto	Statement	volatile	Storage class modifier
if	Statement	while	Statement

Kieåu döõ lieäu char

Moät ñoái töôïng cuûa kieåu char bieåu thò moät kyù töï ñôn öùng vôùi baûng maõ kyù töï 8 bits ASCII.

Bieán kyù töï

char variablename;

hoaëc:

char variablename1, variablename2, variablename3;

Format Kyù töï: %c

Haèng kyù töï

x = `A';
x = 65;

hoaëc

x = `a';
x = 97;

Kyù töï thoùat (\)

Kyù töï	Moâ taû
\b	BACKSPACE
\f	Keát thuùc trang (form-feed)
\r	Xuoáng haøng (RETURN)
\t	TAB

Xuaát caùc kyù töï

Duøng haøm printf(), ñònhnghi4a trong stdio.h, ñeå xuaát leân maøn aûnh.

Ví duï: In caùc kyù töï leân maøn aûnh.

1: /* Printing out characters */
2: #include <stdio.h>
3:
4: main()
5: {
6: char c1;
7: char c2;
8:
9: c1 = `A';
10: c2 = `a';
11: printf("Convert the value of c1 to character: %c.\n", c1);
12: printf("Convert the value of c2 to character: %c.\n", c2);
13: return 0;
14: }
 
Keát quaû:
 
Convert the value of c1 to character: A.
Convert the value of c2 to character: a.

Ví duï: Bieán ñoåi soá thaønh kyù töï (duøng format %c)

1: /* Converting numeric values back to characters */
2: #include <stdio.h>
3:
4: main()
5: {
6: char c1;
7:  char c2;
8:
9: c1 = 65;
10: c2 = 97;
11: printf("The character that has the numeric value of 65 is: %c.\n", c1);
12: printf("The character that has the numeric value of 97 is: %c.\n", c2);
13: return 0;
14: }
 

Keát quaû:
 
The character that has the numeric value of 65 is: A.
The character that has the numeric value of 97 is: a.

Kieåu döõ lieäu int

Döõ lieäu soá khoâng coù thaønh phaàn thaäp phaân. Khoaûng lôùn cuûa noù phuï thuoäc vaøo ñoä daøi boä nhôù löu tröõ.

Soá nguyeân 32 bits : töø 2147483647 (2³¹_1) ñeán -2147483648.
Soá nguyeân 16 bits : töø 32767 (2¹⁵_1) ñeán -32768.

Bieán int

int variablename;
int variablename1, variablename2, variablename3;

Format int: %f

Ví duï: Bieán ñoåi kyù töï thaønh soá (duøng format %d)

1: /* Showing the numeric values of characters */
2: #include <stdio.h>
3:
4: main()
5: {
6: char c1;
7: char c2;
8:
9: c1 = `A';
10: c2 = `a';
11: printf("The numeric value of A is: %d.\n", c1);
12: printf("The numeric value of a is: %d.\n", c2);
13: return 0;
14: }
 

Keát quaû:
The numeric value of A is: 65.
The numeric value of a is: 97.

Kieåu döõ lieäu float

Döõ lieäu soá thöïc bieåu dieãn baèng daáu chaám ñoäng.

Soá thöïc 32 bits: Khoûang giaù trò +/-1.0*10³⁷, coù ít nhaát 6 soá leû thaäp phaân. Caùc pheùp tính giöõ soá thöïc vaø soá thöïc hoaëc vôùi soá nguyeân cho keát quaû kieåu float.

Bieán float

float variablename;
float variablename1, variablename2, variablename3;

Format float: %f

Ví duï: Xuaát keát quaû chia soá int vaø float

1: /* Integer vs. floating-point divisions */
2: #include <stdio.h>
3:
4: main()
5: {
6: int int_num1, int_num2, int_num3; /* Declare integer variables */
7: float flt_num1, flt_num2, flt_num3; /* Declare floating-point variables */
8:
9: int_num1 = 32 / 10; /* Both divisor and dividend are integers */
10: flt_num1 = 32 / 10;
11: int_num2 = 32.0 / 10; /* The divisor is an integer */
12: flt_num2 = 32.0 / 10;
13: int_num3 = 32 / 10.0; /* The dividend is an integer */
14: flt_num3 = 32 / 10.0;
15:
16: printf("The integer divis. of 32/10 is: %d\n", int_num1);
17: printf("The floating-point divis. of 32/10 is: %f\n", flt_num1);
18: printf("The integer divis. of 32.0/10 is: %d\n", int_num2);
19: printf("The floating-point divis. of 32.0/10 is: %f\n", flt_num2);
20: printf("The integer divis. of 32/10.0 is: %d\n", int_num3);
21: printf("The floating-point divis. of 32/10.0 is: %f\n", flt_num3);
22: return 0;
23: }
 

Keát quaû:
 
The integer divis. of 32/10 is: 3
The floating-point divis. of 32/10 is: 3.000000
The integer divis. of 32.0/10 is: 3
The floating-point divis. of 32.0/10 is: 3.200000
The integer divis. of 32/10.0 is: 3
The floating-point divis. of 32/10.0 is: 3.200000

Kieåu döõ lieäu double

Döõ lieäu soá thöïc coù ñoä chính xaùc gaáp ñoâi.

Soá thöïc 64 bits, coù ít nhaát 10 soá leû thaäp phaân.

Bieán double

double variablename;
double variablename1, variablename2, variablename3;

Format double: %e, %E

Quy öôùc ñaët teân bieán

Caùc kyù töï sau ñaây ñöôïc duøng ñaët teân bieán: A-Z, a-z, 0-9 (nhöng khoâng ñöôïc ñaët ñaàu), daáu gaïch döôùi (_).

Bieán khoâng ñöôïc chöùa kyù hieäu toaùn töû.
Bieán khoâng ñöôïc chöùa daáu (.).
Bieán khoâng ñöôïc chöùa (‘).
Bieán khoâng ñöôïc chöùa kyù hieäu ñaëc bieät nhö *, @, #, ?, v.v..

Caûnh baùo

Khoâng bao giôø duøng töø khoùa cuûa C hoaëc teân caùc haøm thö vieän C laøm teân bieán maëc duø coù theå ñöôïc.

Baøi taäp

1. Vieát chöông trình xuaát caùc giaù trò soá cuûa caùc kyù töï Z vaø z..
2. Vieát chöông trình xuaát caùc caùc kyù töï coù giaù trò soá 72 and 104.
3. Cho soá double dbl_num = 123.456;,vieát chöông trình xuaát giaù trò treân theo format float vaø doule.
4. Vieát chöông trình xuaát giaù trò baèng soá cuûa kyù töï xuoáng haøng (\n).

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