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📜 Dart编程-操作员

📅 最后修改于: 2020-11-05 04:14:56 🧑 作者: Mango

表达式是一种特殊的声明，可以求值。每个表达式都由-

操作数-表示数据
运算符-定义如何处理操作数以产生值。

考虑以下表达式–“ 2 + 3”。在此表达式中，2和3是操作数，符号“ +”(加号)是运算符。

在本章中，我们将讨论Dart中可用的运算符。

算术运算符
平等与关系运算符
型式试验操作员
按位运算符
赋值运算符
逻辑运算符

算术运算符

下表显示了Dart支持的算术运算运算符。

Sr.No	Operators & Meaning
1	+ Add
2	− Subtract
3	-expr Unary minus, also known as negation (reverse the sign of the expression)
4	* Multiply
5	/ Divide
6	~/ Divide, returning an integer result
7	% Get the remainder of an integer division (modulo)
8	++ Increment
9	— Decrement

平等和关系运算符

关系运算符测试或定义两个实体之间的关系类型。关系运算符返回布尔值，即true / false。

假设A的值为10，B的值为20。

Operator	Description	Example
>	Greater than	(A > B) is False
<	Lesser than	(A < B) is True
>=	Greater than or equal to	(A >= B) is False
<=	Lesser than or equal to	(A <= B) is True
==	Equality	(A==B) is False
!=	Not equal	(A!=B) is True

型式试验操作员

这些运算符非常方便在运行时检查类型。

Operator	Meaning
is	True if the object has the specified type
is!	False if the object has the specified type

按位运算符

下表列出了Dart中可用的按位运算运算符及其作用-

Operator	Description	Example
Bitwise AND	a & b	Returns a one in each bit position for which the corresponding bits of both operands are ones.
Bitwise OR	a \| b	Returns a one in each bit position for which the corresponding bits of either or both operands are ones.
Bitwise XOR	a ^ b	Returns a one in each bit position for which the corresponding bits of either but not both operands are ones.
Bitwise NOT	~ a	Inverts the bits of its operand.
Left shift	a ≪ b	Shifts a in binary representation b (< 32) bits to the left, shifting in zeroes from the right.
Signpropagating right shift	a ≫ b	Shifts a in binary representation b (< 32) bits to the right, discarding bits shifted off.

赋值运算符

下表列出了Dart中可用的赋值运算符。

Sr.No	Operator & Description
1	=(Simple Assignment ) Assigns values from the right side operand to the left side operand Ex:C = A + B will assign the value of A + B into C
2	??= Assign the value only if the variable is null
3	+=(Add and Assignment) It adds the right operand to the left operand and assigns the result to the left operand. Ex: C += A is equivalent to C = C + A
4	─=(Subtract and Assignment) It subtracts the right operand from the left operand and assigns the result to the left operand. Ex: C -= A is equivalent to C = C – A
5	=(Multiply and Assignment) It multiplies the right operand with the left operand and assigns the result to the left operand. Ex: C = A is equivalent to C = C * A
6	/=(Divide and Assignment) It divides the left operand with the right operand and assigns the result to the left operand.

注–相同的逻辑适用于按位运算符，因此它们将变为＆Lt; =，＆Gt; =，＆Gt; =，＆Gt; =，| =和^ =。

逻辑运算符

逻辑运算符用于组合两个或多个条件。逻辑运算符返回布尔值。假设变量A的值为10，而B为20。

Operator	Description	Example
&&	And − The operator returns true only if all the expressions specified return true	(A > 10 && B > 10) is False.
\|\|	OR − The operator returns true if at least one of the expressions specified return true	(A > 10 \|\| B > 10) is True.
!	NOT − The operator returns the inverse of the expression’s result. For E.g.: !(7>5) returns false	!(A > 10) is True.

条件表达式

Dart有两个运算符，可让您评估可能需要ifelse语句的表达式-

健康)状况 ? expr1：expr2

如果condition为true，则表达式对expr1求值(并返回其值)；否则，表达式为0。否则，它求值并返回expr2的值。

expr1 ?? expr2

如果expr1不为null，则返回其值；否则，返回0。否则，求值并返回expr2的值

例

以下示例显示了如何在Dart中使用条件表达式-

void main() { 
   var a = 10; 
   var res = a > 12 ? "value greater than 10":"value lesser than or equal to 10"; 
   print(res); 
}

它将产生以下输出-

value lesser than or equal to 10

例

让我们再举一个例子-

void main() { 
   var a = null; 
   var b = 12; 
   var res = a ?? b; 
   print(res); 
}

它将产生以下输出-