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<TR> 7 v, T- a4 ~; d<TD class=content>1。4 预定义类型（Predefined types） - D( |2 q) s5 ]8 s F2 N+ J& Q( E' ~; I( @( mc#提供了一系列预定义类型。它们与c/c++有不少相似的地方。预定义引用类型有object和string。 9 g+ \6 ]# j* q+ c
object类型是所有其他类型的基础。 9 m% G% [0 y/ C/ t: g " k5 ]) |- m, G预定义类型包括符号数、无符号数、浮点、布尔、字符和十进制数。符号数有：sbyte、short、 2 w/ W2 U' n/ V
int和long；无符号数有：byte、ushort、uint和ulong；浮点数有：float和double。 " J5 q, ?0 F+ m) k% P& F $ {8 Y* j$ Y. o6 I, Z8 H布尔类型就像一个开关，只有两种状态：true或false。c#对布尔的要求比c/c++严格，与java类似。 . R3 k/ n. L2 h
在c#中false不等于0，true也不等于1；false和true都是单独分离出来的一个值。学过c/c++的网友 % \: Z5 T7 ^/ v1 A- A. T都知道：*/ ' p4 W1 L' D+ ?) f
int i = 0; + ] G; ^; m' v" G1 G6 ~
if (i = 0) { // Bug: 应该是 (i == 0) / D! G! g# B1 }* b" n
.... L! |+ H: s" ` i% @) H; F
} , Z S A& n0 W4 B+ E! ~1 a+ O& J9 `/* 是没有问题的。但在c#中会引发一个编译错误（error CS0029: Cannot implicitly convert ( |% |! w4 S: J! d$ l8 otype 'int' to 'bool'）。当然，这样牺牲了一点没有必要的灵活性。我们再也不能这样：*/ & R! h2 A( Z& r. K# P! N
string str; 7 c" C2 V/ S2 h
.... - N5 N& c, X$ b) Vif(str = Console.ReadLine()) { * J+ {3 [( R. Z
Console.WriteLine("Your comments are: {0}",str); & \ i+ b! }1 ^) d.... 8 g) D1 u1 a4 W8 q- y2 y/* 而必须：*/ 6 q1 y- a2 o; s5 N' F2 @using System; 0 U* \) V! `. e$ l! s$ ~$ kclass BoolTest " V) r; h; p4 O; w2 F7 X7 V3 ^6 R
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static void Main() { ; d( o/ e2 ~2 X' ?3 z string str = Console.ReadLine();//也可以：string str; 1 C# a/ y' m9 G7 r# D if(str == "") // if((str = Console.ReadLine()) == "") ]3 m& [$ I& c0 f0 n% l3 A* U2 U# X7 n
Console.WriteLine("i can't read your comments. Please tell me something! O.K.?"); " x$ L: A: k# s/ F: r
else , I( l2 L, w$ l# i/ ]" x
Console.WriteLine("Your comments are: {0}",str); ! j! ~; C3 M3 \: k, ~( N! @
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我抄了一张预定义类型的简表供大家参考。 " L9 F) J `' I. [9 r( m, ~8 _ I' H, i8 J
Type Description Examples " B/ r& y+ M Q
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object The ultimate base type of all other types object o = new Stack(); 4 {: u0 \* S$ \: s& m# V . |( H1 G; v8 H# n- t5 H0 Y8 z4 `string String type; a string is a sequence of string s = "Hello"; - U: @" I; M' g* M Unicode characters ' n, P- F% @& @. w0 D 0 q) Y* c! g% d% M" i, m" _* @sbyte 8-bit signed integral type sbyte val = 12; 6 A# Z1 M) Q. h }7 l6 S) b! L! i* V/ A
short 16-bit signed integral type short val = 12; 0 d# c( S6 B: L" E4 U7 x/ e4 K$ Y* @8 T/ x6 P; f
int 32-bit signed integral type int val = 12; . {7 G, k3 N: d f! s; l# m
! U% [5 Y0 M9 p) Qlong 64-bit signed integral type long val1 = 12; 8 ]8 H* d" S, L y, q1 C1 O' h long val2 = 34L; 0 }" s$ z# t( i' d0 @( `4 w' N# U2 C7 H3 [/ z- A
byte 8-bit unsigned integral type byte val1 = 12; 6 e7 \3 h1 M. G8 l$ f3 X( f byte val2 = 34U; 0 d$ u& [) q1 V- w3 I
' h. J: ]. W1 J/ |* g& {ushort 16-bit unsigned integral type ushort val1 = 12; " Z, [: P' w( y# |5 [3 @& {
ushort val2 = 34U; ; \% {. d( s& u& b5 e4 h7 \4 |* D
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uint 32-bit unsigned integral type uint val1 = 12; $ ~: W& ^: X& j& o6 N& H
uint val2 = 34U; 3 H& @0 V/ }8 O! h. U 6 ^7 t: L1 O+ L9 I s* B4 b* _ulong 64-bit unsigned integral type ulong val1 = 12; ) ?" E$ T7 W/ } I" Y: @* a. f ulong val2 = 34U; ' T7 E' m% w X. g9 A
ulong val3 = 56L; + A% c. Z' y" ? ulong val4 = 78UL; 9 K, }6 W8 W4 g
1 X: s2 c. [, N+ d: v, |float Single-precision floating point type float value = 1.23F; $ |$ O2 |: E' ?- f1 }
, }+ {/ h! G- p( W. y* D! M! _3 Cdouble Double-precision floating point type double val1 = 1.23 / M( ]* |5 D: O# ^
double val2 = 4.56D; s5 H* X/ u* l' W8 ~- ]: x6 E' y% N! E1 p% u
bool Boolean type; a bool value is either bool value = true; " N) @% o* D4 g9 f8 J" e {" M
true or false h3 g) {# U g* r. L5 o/ H3 x 6 P9 j8 g4 q. ?8 C; f/ c9 `char Character type; a char value is a Unicode char value = 'h'; ! E' ^% q5 m4 O3 n( b character 1 l0 e3 I3 X, V# p& S+ ]5 x+ d
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decimal Precise decimal type with 28 significant digits decimal value = 1.23M; / ]- O+ B6 W5 @0 b, v6 S4 E
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你也可以自定义自己的预定义类型，可以这样：*/ ) D- F( {; K* F1 |2 z5 `# h! Ousing System; 4 Y6 @. P; |, X; z" K$ ~
struct Digit 3 }0 ~( `1 y9 V{...} , V% z+ {, `( \: T
class Test . q! Q1 K2 c7 ?( _0 O{ ! r* P( C/ M% N- `
static void TestInt() { B0 v3 M% i0 n1 n int a = 1; ) Q ]# {( |( q, M2 p5 R) d int b = 2; 2 z/ ?0 p; ~" L1 X( l
int c = a + b; / v O6 U! q. B4 T M! _6 `
Console.WriteLine(c); 9 P) Z% p+ D8 i
} ( B Z3 w2 ]5 U6 m9 ? static void TestDigit() { + f- d! \0 E9 }5 G
Digit a = (Digit) 1; " _4 \# }2 Z, d8 g* u Digit b = (Digit) 2; , s R6 h* I: o. u2 p$ F ]
Digit c = a + b; 1 e; Y( j# k/ N* v3 E! `3 Z Console.WriteLine(c); ! [7 N' O0 r | } 1 z9 H; w) o6 d1 h( S
static void Main() { , j" t5 q. e+ i TestInt(); $ J" o6 B' Y% N# \5 i0 \
TestDigit(); ' J# X' ~; a1 `, K" E$ @# o$ c
} # s; g6 q' `/ {9 V* n5 a5 n; U} {' |' R4 t6 R. v& N" k! m
/* 6 t9 C7 Q; E% R: T/ {: {
这一节有点沉闷。：（ 1 ?- u" {9 f" U5 S0 R! A$ Y! x; a, X% }$ `/ H3 K
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