c++primer学习笔记(1)-primitive buit-in types and type conversions
2014-12-31 00:32
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1.关于 unsigned 的注意事项:
1.unsigned int 可以缩写成 unsigned
2.当用到char类型时,char 有3种形势,char, signed char 和unsigned char , 当我们写char 时,编译器会从signed char 和unsigned char 中选一种。signed char 是 -127 ~ 127, unsigned char 是0 ~ 255
3. 一定不要将unsigned int 类型和signed int 类型进行运算,应为运算过程中,int 会被转化为unsigned int类型,会导致运算结果出错比如int a = -1, unsigned b = 2; a * b != -2;
2.关于literals的注意事项:
1. integer literal有3种情况(下面用表示十进制20来说明):
1. decimal : 20
2. octal : 024
3. hexadecimal : 0x14
2.关于浮点数的表示:
1. 3.14159
2. 3.14159e0 (用E来表示 , 比如3e-2 = 0.03, 3e2 = 300)
3. 12.
(相当于 12.0)
4. .011
3.关于escape sequences(用'\'来表示字符)
1.常见:
backslash :
\\
double quote
: \"
single quote
: \'
2.我们用 \ + 八进制数字 或者 \x + 16进制数字 表示字符;
当,\ 后面跟着超过3位数字时,只有前3位数字表示字符, 而\x 则没有限制
4.关于literal的前缀和后缀
1.字符是+前缀, 数字是+后缀
2.常见字符前缀:
u(Unicode 16 character)
U(Unicode 32 character)
L(wide character)
u8(utf-8(string literals only))
3.常见integer后缀
u or U ( unsigned )
l or L (long)
ll or LL(long long)
4.常见浮点后缀
f or F (float)
l or L (long double)
1.unsigned int 可以缩写成 unsigned
2.当用到char类型时,char 有3种形势,char, signed char 和unsigned char , 当我们写char 时,编译器会从signed char 和unsigned char 中选一种。signed char 是 -127 ~ 127, unsigned char 是0 ~ 255
3. 一定不要将unsigned int 类型和signed int 类型进行运算,应为运算过程中,int 会被转化为unsigned int类型,会导致运算结果出错比如int a = -1, unsigned b = 2; a * b != -2;
2.关于literals的注意事项:
1. integer literal有3种情况(下面用表示十进制20来说明):
1. decimal : 20
2. octal : 024
3. hexadecimal : 0x14
2.关于浮点数的表示:
1. 3.14159
2. 3.14159e0 (用E来表示 , 比如3e-2 = 0.03, 3e2 = 300)
3. 12.
(相当于 12.0)
4. .011
3.关于escape sequences(用'\'来表示字符)
1.常见:
backslash :
\\
double quote
: \"
single quote
: \'
2.我们用 \ + 八进制数字 或者 \x + 16进制数字 表示字符;
当,\ 后面跟着超过3位数字时,只有前3位数字表示字符, 而\x 则没有限制
4.关于literal的前缀和后缀
1.字符是+前缀, 数字是+后缀
2.常见字符前缀:
u(Unicode 16 character)
U(Unicode 32 character)
L(wide character)
u8(utf-8(string literals only))
3.常见integer后缀
u or U ( unsigned )
l or L (long)
ll or LL(long long)
4.常见浮点后缀
f or F (float)
l or L (long double)
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