user-0 提问: 请教一个C语言问题！

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user: user-1
content: //C++ Operators //  Operators specify an evaluation to be performed on one of the following: //    One operand (unary operator) //    Two operands (binary operator) //    Three operands (ternary operator) //  The C++ language includes all C operators and adds several new operators. //  Table 1.1 lists the operators available in Microsoft C++. //  Operators follow a strict precedence which defines the evaluation order of //expressions containing these operators.  Operators associate with either the //expression on their left or the expression on their right;    this is called //“associativity.” Operators in the same group have equal precedence and are //evaluated left to right in an expression unless explicitly forced by a pair of //parentheses, ( ). //  Table 1.1 shows the precedence and associativity of C++ operators //  (from highest to lowest precedence). // //Table 1.1   C++ Operator Precedence and Associativity // The highest precedence level is at the top of the table. //+------------------+-----------------------------------------+---------------+ //| Operator         | Name or Meaning                         | Associativity | //+------------------+-----------------------------------------+---------------+ //| ::               | Scope resolution                        | None          | //| ::               | Global                                  | None          | //| [ ]              | Array subscript                         | Left to right | //| ( )              | Function call                           | Left to right | //| ( )              | Conversion                              | None          | //| .                | Member selection (object)               | Left to right | //| ->               | Member selection (pointer)              | Left to right | //| ++               | Postfix increment                       | None          | //| --               | Postfix decrement                       | None          | //| new              | Allocate object                         | None          | //| delete           | Deallocate object                       | None          | //| delete[ ]        | Deallocate object                       | None          | //| ++               | Prefix increment                        | None          | //| --               | Prefix decrement                        | None          | //| *                | Dereference                             | None          | //| &                | Address-of                              | None          | //| +                | Unary plus                              | None          | //| -                | Arithmetic negation (unary)             | None          | //| !                | Logical NOT                             | None          | //| ~                | Bitwise complement                      | None          | //| sizeof           | Size of object                          | None          | //| sizeof ( )       | Size of type                            | None          | //| typeid( )        | type name                               | None          | //| (type)           | Type cast (conversion)                  | Right to left | //| const_cast       | Type cast (conversion)                  | None          | //| dynamic_cast     | Type cast (conversion)                  | None          | //| reinterpret_cast | Type cast (conversion)                  | None          | //| static_cast      | Type cast (conversion)                  | None          | //| .*               | Apply pointer to class member (objects) | Left to right | //| ->*              | Dereference pointer to class member     | Left to right | //| *                | Multiplication                          | Left to right | //| /                | Division                                | Left to right | //| %                | Remainder (modulus)                     | Left to right | //| +                | Addition                                | Left to right | //| -                | Subtraction                             | Left to right | //| <<               | Left shift                              | Left to right | //| >>               | Right shift                             | Left to right | //| <                | Less than                               | Left to right | //| >                | Greater than                            | Left to right | //| <=               | Less than or equal to                   | Left to right | //| >=               | Greater than or equal to                | Left to right | //| ==               | Equality                                | Left to right | //| !=               | Inequality                              | Left to right | //| &                | Bitwise AND                             | Left to right | //| ^                | Bitwise exclusive OR                    | Left to right | //| |                | Bitwise OR                              | Left to right | //| &&               | Logical AND                             | Left to right | //| ||               | Logical OR                              | Left to right | //| e1?e2:e3         | Conditional                             | Right to left | //| =                | Assignment                              | Right to left | //| *=               | Multiplication assignment               | Right to left | //| /=               | Division assignment                     | Right to left | //| %=               | Modulus assignment                      | Right to left | //| +=               | Addition assignment                     | Right to left | //| -=               | Subtraction assignment                  | Right to left | //| <<=              | Left-shift assignment                   | Right to left | //| >>=              | Right-shift assignment                  | Right to left | //| &=               | Bitwise AND assignment                  | Right to left | //| |=               | Bitwise inclusive OR assignment         | Right to left | //| ^=               | Bitwise exclusive OR assignment         | Right to left | //| ,                | Comma                                   | Left to right | //+------------------+-----------------------------------------+---------------+

user: user-2
content: scanf如果输入成功有一个返回值，输入错误也会有一个返回值，可以定义int a=scanf(。。。)查看返回值。

user: user-3
content: ～是按位取反，scanf对返回值的操作； EOF是-1，按位取反就是0了；

user: user-4
content: 关键你要弄懂scanf返回值的意思，表示的成功接收到的数目，如果失败，返回的是EOF，也就是0xFFFFFFFF，这个值取反以后就是0  参看：http://en.cppreference.com/w/c/io/fscanf

user: user-0
content: 引用 4楼列子汤问 的回复:scanf的返回值是 输入变量的个数。 如果输入了a和b那么就返回2. ~scanf()，就是没有得到正确输入 总体上就是，如果有正确输入，就退出循环，如果没有正确输入，就执行循环，一直取值。明白了 谢谢！

user: user-0
content: 引用 3楼shabby0104 的回复:scanf这个函数是有返回值的，返回时参数的个数。 ~是按位取反 while后面括号里只要非0就会一直循环，除非break 这句话的意思的是只要有输入就会一直循环下去谢谢！

user: user-5
content: scanf的返回值是 输入变量的个数。 如果输入了a和b那么就返回2. ~scanf()，就是没有得到正确输入 总体上就是，如果有正确输入，就退出循环，如果没有正确输入，就执行循环，一直取值。

user: user-6
content: scanf这个函数是有返回值的，返回时参数的个数。 ~是按位取反 while后面括号里只要非0就会一直循环，除非break 这句话的意思的是只要有输入就会一直循环下去

user: user-0
content: 引用 1楼小灸舞 的回复:scanf的返回值是接收到的变量值的个数 而~是位运算，取反能在解释清楚点吗谢谢！

user: user-7
content: scanf的返回值是接收到的变量值的个数 而~是位运算，取反