int and larger values are type long. By adding a suffix, we can force the type of a literal integer constant to be type long or unsigned or unsigned long. We specify that a constant is a long by immediately following the value with either L or l (the letter “ell” in either uppercase or lowercase).

根据语法， 八进制或十六进制的整数字面常量有可能是unsigned 类型（unsigned int 或unsignedlong），而十进制的整数字面常量只能是int 或long 类型。不过代码中还是直接以后缀标明类型为佳。

When specifying a long, use the uppercase L: the lowercase letter l is too easily mistaken for the digit 1.

In a similar manner, we can specify unsigned by following the literal with either U or u. We can obtain an unsigned long literal constant by following the value by both L and U. The suffix must appear with no intervening space:

128u /* unsigned */ 1024UL /* unsigned long */ 
1L /* long */ 8Lu /* unsigned long */ 

There are no literals of type short.

注意：整数字面常量没有负数，代码中出现的形如“-1”的数是个表达式，表示1 这个字面常量的相反数（详见第5.1 节：一元取反操作符）。

Rules for Floating-Point Literals

We can use either common decimal notation or scientific notation to write floatingpoint literal constants. Using scientific notation, the exponent is indicated either by E or e. By default, floating-point literals are type double. We indicate single
precision by following the value with either F or f. Similarly, we specify extended precision by following the value with either L or l (again, use of the lowercase l is discouraged). Each pair of literals below denote the same underlying value:

3.14159F .001f 12.345L 0.
3.14159E0f 1E-3F 1.2345E1L 0e0

Boolean and Character Literals

The words true and false are literals of type bool:

bool test = false; 

Printable character literals are written by enclosing the character within single quotation marks:

'a'   '2'   ','  ' ' // blank 

注意：一对单引号之间只能有一个字符，否则编译器会给出警告。