my学习OC--运算符&表达式&语句

运算符

运算符是一个符号，它告诉编译器执行特定的数学或逻辑操作。Objective-C语言有丰富的内置运算符并提供了以下几种类型：

算术运算符关系运算符逻辑运算符位运算符赋值运算符其它运算符

算术运算符

表2.3列出了所有支持Objective-C语言的算术运算符。假设变量A=10，变量B=20，则：

运算符描述示例+adds two operandsA + B will give 30-subtracts second operands from the firstA - B will give -10*multiplies both operandsA * B will give 200/divides numerator by denominatorB / A will give 2%modulus operator and remainder of after an integer divisionB % A will give 0++Increment operator increases integer value by oneA ++ will give 11--decrement operator decreases integer value by oneA -- will give 9

关系运算符

表2.4列出了所有支持Objective-C语言的关系运算符。假设变量A=10，变量B=20，则：

运算符描述示例==checks if the values of two operands are equal or not; if yes, then condition becomes true（A == B）is not true!=checks if the values of two operands are equal or not; if values are not equal, then condition becomes true（A != B）is true>checks if the values of left operands is greater than value of right operand; if yes, then codition becomes true（A > B）is not true<checks if the values of left operands is less than value of right operand; if yes, then codition becomes true（A < B）is true>=checks if the values of left operands is greater than or equal to the value of right operand; if yes, then codition becomes true（A >= B）is not true<=checks if the values of left operands is less than or equal to the value of right operand; if yes, then codition becomes true（A <= B）is true

逻辑运算符

表2.5列出了所有支持Objective-C语言的逻辑运算符。假设变量A=1，变量B=0，则：

运算符描述示例&&called Logical AND Operator. If both the operands are non zero then condition becomes true（A && B）is false││called Logical OR Operator. If any of the two operands is non zero then condition becomes true（A││B）is true!called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true, then Logical NOT operator will make false（A ! B）is true

位运算符

表2.6列出了所有支持Objective-C语言的位运算符。假设变量A=60，变量B=13，二进制为A=0011 1100，B=0000 1101，则：

运算符描述示例&Binary AND Operator copies a bit to the result if it exists in both operands.（A & B）will give 12, which is 0000 1100│Binary OR Operator copies a bit if it exists in either operands.（A │ B）will give 61, which is 0011 1101^Binary XOR Operator copies the bit if it set in one operand but not both.（A ^ B）will give 49, which is 0011 0001~Binary Ones Complement Operator is unary and has the effect of 'flipping' bits.（~ A）will give -61, which is 1100 0011 in 2's complement form<<Binary Left Shift Operator. The left operands value is moved left by number of bits specified by the right operand.（A << 2）will give 240, which is 1111 0000>>Binary Right Shift OPerator. The left operands value is moved right by the number of bits specified by the right operand.（A >> 2）will give 15, which is 0000 1111

赋值运算符

表2.7列出了Objective-C语言所有支持的赋值运算符：

运算符描述示例=Simple assignment operator, assigns values from right side operands to left side operandC = A + B wll assign value of A + B into C+=Add AND assignment operator, it adds right operand to the left operand and assigns the result to left operandC += A is equivalent to C = C + A-=Subtract AND assignment operator, it subtract right operand from the left operand and assigns the result to left operandC -= A is equivalent to C = C - A*=Multipy AND assignment operator, it multipies right operand with the left operand and assigns the result to left operandC = A is equivalent to C = C A/=Divide AND assignment operator, it divides left operand with the right operand and assigns the result to left operandC /= A is equivalent to C = C / A%=Modulus And assignment operator, it takes modulus using two operands and assigns the result to left operandC %= A is equivalent to C = C % A<<=Left shift AND assignment operatorC <<= 2 is same as C = C << 2>>=Right shift AND assignment operatorC >>= 2 is same as C = C >> 2&=Bitwise AND assignment operatorC &= 2 is same as C = C & 2^=Bitwise exclusive OR and assignment operatorC ^= 2 is same as C = C ^ 2l=Bitwise inclusive OR and assignment operatorC l= 2 is same as C = C l 2

其它运算符

表2.8列出了一些其它重要的运算符，包括sizeof和?:运算符：

运算符描述示例sizeof()return the size of an variablesizeof(a), where a is integer, will return 4&return the address of an variable&a; will give actual address of the address*yiibaier to variable*a; will yiibaier to a variable? :conditional expreeionIf condition is true ? Then value X : otherwise value Y

运算符优先级

表2.9整理了运算符的优先级。在这里，运算符具有最高优先级则出现在上面的表中，那些低优先级的则出现在表的底部。在一个表达式中，优先级较高的运算符将首先计算。

优先级运算符名称或含义使用形式结合方向说明1[]数组下标数组名[常量表达式]左到右——-()圆括号（表达式）/函数名(形参表)左到右——-.成员选择（对象）对象.成员名左到右——-->成员选择（指针）对象指针->成员名左到右——2-负号运算符-表达式右到左单目运算符-(类型)强制类型转换(数据类型)表达式右到左——-++自增运算符++变量名/变量名++右到左单目运算符---自减运算符--变量名/变量名--右到左单目运算符-*取值运算符*指针变量右到左单目运算符-&取地址运算符&变量名右到左单目运算符-!逻辑非运算符!表达式右到左单目运算符-~按位取反运算符~表达式右到左单目运算符-sizeof长度运算符sizeof(表达式)右到左——3/除表达式/表达式左到右双目运算符-*乘表达式*表达式左到右双目运算符-%余数（取模）整型表达式/整型表达式左到右双目运算符4+加表达式+表达式左到右双目运算符--减表达式-表达式左到右双目运算符5<<左移变量<<表达式左到右双目运算符->>右移变量>>表达式左到右双目运算符6>大于表达式>表达式左到右双目运算符->=大于等于表达式>=表达式左到右双目运算符-<小于表达式<表达式左到右双目运算符-<=小于等于表达式<=表达式左到右双目运算符7==等于表达式==表达式左到右双目运算符-! =不等于表达式 ! = 表达式左到右双目运算符8&按位与表达式&表达式左到右双目运算符9^按位异或表达式^表达式左到右双目运算符10l按位或表达式l表达式左到右双目运算符11&&逻辑与表达式&&表达式左到右双目运算符12ll逻辑或表达式ll表达式左到右双目运算符13?:条件运算符表达式1? 表达式2: 表达式3右到左三目运算符14=赋值运算符变量=表达式右到左——-/=除后赋值变量/=表达式右到左——-*=乘后赋值变量*=表达式右到左——-%=取模后赋值变量%=表达式右到左——-+=加后赋值变量+=表达式右到左——--=减后赋值变量-=表达式右到左——-<<=左移后赋值变量<<=表达式右到左——->>=右移后赋值变量>>=表达式右到左——-&=按位与后赋值变量&=表达式右到左——-^=按位异或后赋值变量^=表达式右到左——-l=按位或后赋值变量l= 表达式右到左——15,逗号运算符表达式,表达式,…左到右从左向右顺序运算

说明：除了赋值运算符和单目运算符以及条件运算符外（?: ）外，所有的运算符都是向左关联的。优先级从上到下依次递减，最上面具有最高的优先级，逗号操作符具有最低的优先级。相同优先级中，按结合顺序计算。基本的优先级需要记住：

指针最优，单目运算优于双目运算。如正负号。先乘除（模），后加减。先算术运算，后移位运算，最后位运算。请特别注意：1 << 3 + 2 & 7等价于 (1 << (3 + 2))&7.逻辑运算最后计算。

表达式

表达式，是由数字、算符、数字分组符号（括号）、自由变量和约束变量等以能求得数值的有意义排列方法所得的组合。如：算术表达式、逻辑表达式、关系表达式、赋值表达式、逗号表达式等等。

参考： 1.   Objective-C 学习笔记 - 第2章 数据类型、运算符和表达式      http://www.jianshu.com/p/88edda182683 2.   OC中的数据类型和运算符 http://blog.csdn.net/tangjun201/article/details/45563125