在课本上看到一个例题，里面给double变量初始化为1.0了，我想知道能不能直接初始化为1（double = 1；）啊？结果好像都一样，我想知道写成小数是有什么特别的目的吗？
感谢回答！
double a = 1也是可以的
但由于1为默认为int型，因此double a=1实际上还需要进行一次类型转换。写成double a=1.0则不需要
c语言里面，浮点型分为float和double两种类型
float a ＝0这也可行，但是，这在可能会在后面的操作使用时出问题。
float a ＝0.0f是在告诉系统，这是一个浮点数，系统默认浮点型为double，后面加f是告诉系统是float类型的数。
double b ＝ 0.0，double类型直接定义即可。
float ret ＝ 5 / 2
和
float ret ＝ 5/2.0的结果是不一样的
C++ Integer Constants
Integer constants are constant data elements that have no fractional parts or exponents. They always begin with a digit. You can specify integer constants in decimal, octal, or hexadecimal form. They can specify signed or unsigned types and long or short types.
Syntax
integer-constant :
decimal-constant integer-suffixopt
octal-constant integer-suffixopt
hexadecimal-constant integer-suffixopt
'c-char-sequence'
decimal-constant :
nonzero-digit
decimal-constant digit
octal-constant :
0
octal-constant octal-digit
hexadecimal-constant :
0x hexadecimal-digit
0X hexadecimal-digit
hexadecimal-constant hexadecimal-digit
nonzero-digit : one of
1 2 3 4 5 6 7 8 9
octal-digit : one of
0 1 2 3 4 5 6 7
hexadecimal-digit : one of
0 1 2 3 4 5 6 7 8 9
a b c d e f
A B C D E F
integer-suffix :
unsigned-suffix long-suffixopt
long-suffix unsigned-suffixopt
unsigned-suffix : one of
u U
long-suffix : one of
l L
64-bit integer-suffix :
i64
To specify integer constants using octal or hexadecimal notation, use a prefix that denotes the base. To specify an integer constant of a given integral type, use a suffix that denotes the type.
To specify a decimal constant, begin the specification with a nonzero digit. For example:
int i = 157; // Decimal constant
int j = 0198; // Not a decimal number; erroneous octal constant
int k = 0365; // Leading zero specifies octal constant, not decimal
To specify an octal constant, begin the specification with 0, followed by a sequence of digits in the range 0 through 7. The digits 8 and 9 are errors in specifying an octal constant. For example:
int i = 0377; // Octal constant
int j = 0397; // Error: 9 is not an octal digit
To specify a hexadecimal constant, begin the specification with 0x or 0X (the case of the “x” does not matter), followed by a sequence of digits in the range 0 through 9 and a (or A) through f (or F). Hexadecimal digits a (or A) through f (or F) represent values in the range 10 through 15. For example:
int i = 0x3fff; // Hexadecimal constant
int j = 0X3FFF; // Equal to i
To specify an unsigned type, use either the u or U suffix. To specify a long type, use either the l or L suffix. For example:
unsigned uVal = 328u; // Unsigned value
long lVal = 0x7FFFFFL; // Long value specified
// as hex constant
unsigned long ulVal = 0776745ul; // Unsigned long value
C++ Floating-Point Constants
Floating-point constants specify values that must have a fractional part. These values contain decimal points (.) and can contain exponents.
Syntax
floating-constant :
fractional-constant exponent-partopt floating-suffixopt
digit-sequence exponent-part floating-suffixopt
fractional-constant :
digit-sequenceopt . digit-sequence
digit-sequence .
exponent-part :
e signopt digit-sequence
E signopt digit-sequence
sign : one of
digit-sequence :
digit
digit-sequence digit
floating-suffix :one of
f l F L
Floating-point constants have a “mantissa,” which specifies the value of the number, an “exponent,” which specifies the magnitude of the number, and an optional suffix that specifies the constant’s type. The mantissa is specified as a sequence of digits followed by a period, followed by an optional sequence of digits representing the fractional part of the number. For example:
18.46
38.
The exponent, if present, specifies the magnitude of the number as a power of 10, as shown in the following example:
18.46e0 // 18.46
18.46e1 // 184.6
If an exponent is present, the trailing decimal point is unnecessary in whole numbers such as 18E0.
Floating-point constants default to type double. By using the suffixes f or l (or F or L — the suffix is not case sensitive), the constant can be specified as float or long double, respectively.
Although long double and double have the same representation, they are not the same type. For example, you can have overloaded functions like
void func( double );
and
void func( long double );