• [Objective-C语言教程]关系运算符(8)


    运算符是一个符号,告诉编译器执行特定的数学或逻辑操作。 Objective-C语言内置很多运算符,提供如下类型的运算符 -

    • 算术运算符
    • 关系运算符
    • 逻辑运算符
    • 按位运算符
    • 分配运算符
    • 其它运算符

    本教程将逐一解释算术,关系,逻辑,按位,赋值和其他运算符。

    1. 算术运算符

    下表显示了Objective-C语言支持的所有算术运算符。 假设变量A=10,变量B=20,则 -

    运算符描述示例
    + 两个操作数相加 A + B = 30
    - 从第一个减去第二个操作数 A - B = -10
    * 两个操作数相乘 A * B = 200
    / 分子除以分母 B / A = 2
    % 模数运算符,整数除法后的余数 B % A = 0
    ++ 递增运算符,将整数值增加1 A++,结果为11
    -- 递减运算符,将整数值减1 A--,结果为9

    算术运算符示例

     1 #import <Foundation/Foundation.h>
     2 
     3 int main() {
     4    int a = 21;
     5    int b = 10;
     6    int c ;
     7 
     8    c = a + b;
     9    NSLog(@"Line 1 - Value of c is %d
    ", c );
    10    c = a - b;
    11    NSLog(@"Line 2 - Value of c is %d
    ", c );
    12    c = a * b;
    13    NSLog(@"Line 3 - Value of c is %d
    ", c );
    14    c = a / b;
    15    NSLog(@"Line 4 - Value of c is %d
    ", c );
    16    c = a % b;
    17    NSLog(@"Line 5 - Value of c is %d
    ", c );
    18    c = a++; 
    19    NSLog(@"Line 6 - Value of c is %d
    ", c );
    20    c = a--; 
    21    NSLog(@"Line 7 - Value of c is %d
    ", c );
    22 }

    执行上面示例代码,得到以下结果:

    1 2018-11-14 04:55:08.592 main[143613] Line 1 - Value of c is 31
    2 2018-11-14 04:55:08.593 main[143613] Line 2 - Value of c is 11
    3 2018-11-14 04:55:08.593 main[143613] Line 3 - Value of c is 210
    4 2018-11-14 04:55:08.593 main[143613] Line 4 - Value of c is 2
    5 2018-11-14 04:55:08.593 main[143613] Line 5 - Value of c is 1
    6 2018-11-14 04:55:08.593 main[143613] Line 6 - Value of c is 21
    7 2018-11-14 04:55:08.593 main[143613] Line 7 - Value of c is 22

    2. 关系运算符

    下表显示了Objective-C语言支持的所有关系运算符。假设变量A=10,变量B=20,则 -

    运算符描述示例
    == 比较两个操作数的值是否相等; 如果相等,则条件成立。 (A == B)结果为:false
    != 比较两个操作数的值是否相等; 如果不相等,则条件成立。 (A != B)结果为:true
    > 比较左操作数的值是否大于右操作数的值; 如果是,则条件成立。 (A > B)结果为:false
    < 比较左操作数的值是否小于右操作数的值; 如果是,则条件成立。 (A < B)结果为:true
    >= 比较左操作数的值是否大于等于右操作数的值; 如果是,则条件成立。 (A >= B)结果为:false
    <= 比较左操作数的值是否小于等于右操作数的值; 如果是,则条件成立。 (A <= B)结果为:true

    关系运算符示例

     1  Live Demo
     2 #import <Foundation/Foundation.h>
     3 
     4 int main() {
     5    int a = 21;
     6    int b = 10;
     7 
     8    if( a == b ) {
     9       NSLog(@"Line 1 - a is equal to b
    " );
    10    } else {
    11       NSLog(@"Line 1 - a is not equal to b
    " );
    12    }
    13 
    14    if ( a < b ) {
    15       NSLog(@"Line 2 - a is less than b
    " );
    16    } else {
    17       NSLog(@"Line 2 - a is not less than b
    " );
    18    } 
    19 
    20    if ( a > b ) {
    21       NSLog(@"Line 3 - a is greater than b
    " );
    22    } else {
    23       NSLog(@"Line 3 - a is not greater than b
    " );
    24    }
    25 
    26    /* Lets change value of a and b */
    27    a = 5;
    28    b = 20;
    29 
    30    if ( a <= b ) {
    31       NSLog(@"Line 4 - a is either less than or equal to  b
    " );
    32    }
    33 
    34    if ( b >= a ) {
    35       NSLog(@"Line 5 - b is either greater than  or equal to b
    " );
    36    }
    37 }

    执行上面示例代码,得到以下结果:

    1 2018-11-14 05:01:20.415 main[49282] Line 1 - a is not equal to b
    2 2018-11-14 05:01:20.417 main[49282] Line 2 - a is not less than b
    3 2018-11-14 05:01:20.417 main[49282] Line 3 - a is greater than b
    4 2018-11-14 05:01:20.417 main[49282] Line 4 - a is either less than or equal to  b
    5 2018-11-14 05:01:20.417 main[49282] Line 5 - b is either greater than  or equal to b

    3. 逻辑运算符

    下表显示了Objective-C语言支持的所有逻辑运算符。 假设变量A=1,而变量B=0,则 -

    运算符描述示例
    && 逻辑“与”运算符。 如果两个操作数都不为零,则条件成立。 (A && B)结果为:false
    ΙΙ 逻辑“或”运算符。如果两个操作数中的任何一个不为零,则条件变为true (A ΙΙ B)结果为:true
    ! 逻辑“非”运算符。 用于反转其操作数的逻辑状态。 如果条件为true,则逻辑“非”运算符后将为false !(A && B)结果为:true

    逻辑运算符示例

     1 #import <Foundation/Foundation.h>
     2 
     3 int main() {
     4    int a = 5;
     5    int b = 20;
     6 
     7    if ( a && b ) {
     8       NSLog(@"Line 1 - Condition is true
    " );
     9    }
    10 
    11    if ( a || b ) {
    12       NSLog(@"Line 2 - Condition is true
    " );
    13    }
    14 
    15    /* lets change the value of  a and b */
    16    a = 0;
    17    b = 10;
    18 
    19    if ( a && b ) {
    20       NSLog(@"Line 3 - Condition is true
    " );
    21    } else {
    22       NSLog(@"Line 3 - Condition is not true
    " );
    23    }
    24 
    25    if ( !(a && b) ) {
    26       NSLog(@"Line 4 - Condition is true
    " );
    27    }
    28 }

    执行上面示例代码,得到以下结果:

    1 2018-11-14 05:07:48.922 main[33387] Line 1 - Condition is true
    2 2018-11-14 05:07:48.924 main[33387] Line 2 - Condition is true
    3 2018-11-14 05:07:48.924 main[33387] Line 3 - Condition is not true
    4 2018-11-14 05:07:48.924 main[33387] Line 4 - Condition is true

    4. 按位运算符

    按位运算符处理位并执行逐位运算。 |^的真值表如下 -

    假设A = 60B = 13,现在以二进制格式,它们按位运算将如下 -

    A = 0011 1100
    
    B = 0000 1101
    
    -----------------
    
    A&B = 0000 1100
    
    A|B = 0011 1101
    
    A^B = 0011 0001
    
    ~A  = 1100 0011
    

    Objective-C语言支持按位运算符。假设变量A=60,变量B=13,如下表所示 -

    运算符描述示例
    & 二进制AND运算符,如果两个操作数同位上存在1,则它会将结果复制到结果中。 (A & B) = 12, 也就是:0000 1100
    Ι 二进制OR运算符,如果存在于任一操作数中,则复制1位。 (A Ι B) = 12 , 也就是:0011 1101
    ^ 二进制异或运算符,如果在一个操作数中设置,但不在两个操作数中设置,则复制该位。 (A ^ B) = 49, 也就是:0011 0001
    ~ 二元补语运算符是一元的,具有“翻转”位的效果。 (~A )结果为:-61, 也就是:1100 0011
    << 二进制左移运算符。左操作数值向左移动右操作数指定的位数。 A << 2 = 240, 也就是:1111 0000
    >> 二进制右移运算符。左操作数值向右移动右操作数指定的位数。 A >> 2 = 15, 也就是:0000 1111

    按位运算符示例

     1 #import <Foundation/Foundation.h>
     2 
     3 int main() {
     4    unsigned int a = 60;    /* 60 = 0011 1100 */  
     5    unsigned int b = 13;    /* 13 = 0000 1101 */
     6    int c = 0;           
     7 
     8    c = a & b;          /* 12 = 0000 1100 */ 
     9    NSLog(@"Line 1 - Value of c is %d
    ", c );
    10 
    11    c = a | b;           /* 61 = 0011 1101 */
    12    NSLog(@"Line 2 - Value of c is %d
    ", c );
    13 
    14    c = a ^ b;           /* 49 = 0011 0001 */
    15    NSLog(@"Line 3 - Value of c is %d
    ", c );
    16 
    17    c = ~a;              /*-61 = 1100 0011 */
    18    NSLog(@"Line 4 - Value of c is %d
    ", c );
    19 
    20    c = a << 2;          /* 240 = 1111 0000 */
    21    NSLog(@"Line 5 - Value of c is %d
    ", c );
    22 
    23    c = a >> 2;          /* 15 = 0000 1111 */
    24    NSLog(@"Line 6 - Value of c is %d
    ", c );
    25 }

    执行上面示例代码,得到以下结果结果:

    1 2018-11-14 05:10:38.700 main[158736] Line 1 - Value of c is 12
    2 2018-11-14 05:10:38.702 main[158736] Line 2 - Value of c is 61
    3 2018-11-14 05:10:38.702 main[158736] Line 3 - Value of c is 49
    4 2018-11-14 05:10:38.702 main[158736] Line 4 - Value of c is -61
    5 2018-11-14 05:10:38.702 main[158736] Line 5 - Value of c is 240
    6 2018-11-14 05:10:38.702 main[158736] Line 6 - Value of c is 15

    5. 赋值运算符

    Objective-C语言支持以下赋值运算符 -

    运算符描述示例
    = 简单赋值运算符,将右侧操作数的值分配给左侧操作数 C = A + B是将A + B的值分配给C
    += 相加和赋值运算符,它将右操作数添加到左操作数并将结果赋给左操作数 C += A 相当于 C = C + A
    -= 相减和赋值运算符,它从左操作数中减去右操作数,并将结果赋给左操作数 C -= A 相当于 C = C - A
    *= 相乘和赋值运算符,它将右操作数与左操作数相乘,并将结果赋给左操作数 C *= A 相当于 C = C * A
    /= 除以和赋值运算符,它将左操作数除以右操作数,并将结果赋给左操作数 C /= A 相当于 C = C / A
    %= 模数和赋值运算符,它使用两个操作数获取模数,并将结果赋给左操作数 C %= A 相当于 C = C % A
    <<= 左移和赋值运算符 C <<= 2 相当于 C = C << 2
    >>= 右移和赋值运算符 C >>= 2 相当于 C = C >> 2
    &= 按位并赋值运算符 C &= 2 相当于 C = C & 2
    ^= 按位异或和赋值运算符 C ^= 2 相当于 C = C ^ 2
    Ι 按位包含OR和赋值运算符 C Ι= 2 相当于 C = C Ι 2

    赋值运算符示例

     1 #import <Foundation/Foundation.h>
     2 
     3 int main() {
     4    int a = 21;
     5    int c ;
     6 
     7    c =  a;
     8    NSLog(@"Line 1 - =  Operator Example, Value of c = %d
    ", c );
     9 
    10    c +=  a;
    11    NSLog(@"Line 2 - += Operator Example, Value of c = %d
    ", c );
    12 
    13    c -=  a;
    14    NSLog(@"Line 3 - -= Operator Example, Value of c = %d
    ", c );
    15 
    16    c *=  a;
    17    NSLog(@"Line 4 - *= Operator Example, Value of c = %d
    ", c );
    18 
    19    c /=  a;
    20    NSLog(@"Line 5 - /= Operator Example, Value of c = %d
    ", c );
    21 
    22    c  = 200;
    23    c %=  a;
    24    NSLog(@"Line 6 - %= Operator Example, Value of c = %d
    ", c );
    25 
    26    c <<=  2;
    27    NSLog(@"Line 7 - <<= Operator Example, Value of c = %d
    ", c );
    28 
    29    c >>=  2;
    30    NSLog(@"Line 8 - >>= Operator Example, Value of c = %d
    ", c );
    31 
    32    c &=  2;
    33    NSLog(@"Line 9 - &= Operator Example, Value of c = %d
    ", c );
    34 
    35    c ^=  2;
    36    NSLog(@"Line 10 - ^= Operator Example, Value of c = %d
    ", c );
    37 
    38    c |=  2;
    39    NSLog(@"Line 11 - |= Operator Example, Value of c = %d
    ", c );
    40 
    41 }

    执行上面示例代码,得到以下结果:

     1 2018-11-14 05:14:03.383 main[149970] Line 1 - =  Operator Example, Value of c = 21
     2 2018-11-14 05:14:03.385 main[149970] Line 2 - += Operator Example, Value of c = 42
     3 2018-11-14 05:14:03.385 main[149970] Line 3 - -= Operator Example, Value of c = 21
     4 2018-11-14 05:14:03.385 main[149970] Line 4 - *= Operator Example, Value of c = 441
     5 2018-11-14 05:14:03.385 main[149970] Line 5 - /= Operator Example, Value of c = 21
     6 2018-11-14 05:14:03.385 main[149970] Line 6 - %= Operator Example, Value of c = 11
     7 2018-11-14 05:14:03.385 main[149970] Line 7 - <<= Operator Example, Value of c = 44
     8 2018-11-14 05:14:03.385 main[149970] Line 8 - >>= Operator Example, Value of c = 11
     9 2018-11-14 05:14:03.385 main[149970] Line 9 - &= Operator Example, Value of c = 2
    10 2018-11-14 05:14:03.385 main[149970] Line 10 - ^= Operator Example, Value of c = 0
    11 2018-11-14 05:14:03.385 main[149970] Line 11 - |= Operator Example, Value of c = 2

    6. 其他运算符:sizeof和三元运算符

    还有其他一些重要的运算符,包括sizeof?:三元运算符,Objective-C语言也都支持。

    运算符描述示例
    sizeof() 返回变量的大小 sizeof(a), 这里如果变量a是整数,则将返回:4
    & 返回变量的地址。 &a将返回变量的实际地址。
    * 指向变量的指针。 *a将指向变量。
    ? : 条件表达式 如果条件为真?然后是X值:否则为Y

    sizeof和三元运算符示例

     1 #import <Foundation/Foundation.h>
     2 
     3 int main() {
     4    int a = 4;
     5    short b;
     6    double c;
     7    int* ptr;
     8 
     9    /* example of sizeof operator */
    10    NSLog(@"Line 1 - Size of variable a = %d
    ", sizeof(a) );
    11    NSLog(@"Line 2 - Size of variable b = %d
    ", sizeof(b) );
    12    NSLog(@"Line 3 - Size of variable c= %d
    ", sizeof(c) );
    13 
    14    /* example of & and * operators */
    15    ptr = &a;    /* 'ptr' now contains the address of 'a'*/
    16    NSLog(@"value of a is  %d
    ", a);
    17    NSLog(@"*ptr is %d.
    ", *ptr);
    18 
    19    /* example of ternary operator */
    20    a = 10;
    21    b = (a == 1) ? 20: 30;
    22    NSLog(@"Value of b is %d
    ", b );
    23 
    24    b = (a == 10) ? 20: 30;
    25    NSLog(@"Value of b is %d
    ", b );
    26 }

    执行上面示例代码,得到以下结果:

    1 2018-11-14 05:18:49.270 main[174436] Line 1 - Size of variable a = 4
    2 2018-11-14 05:18:49.271 main[174436] Line 2 - Size of variable b = 2
    3 2018-11-14 05:18:49.271 main[174436] Line 3 - Size of variable c= 8
    4 2018-11-14 05:18:49.271 main[174436] value of a is  4
    5 2018-11-14 05:18:49.271 main[174436] *ptr is 4.
    6 2018-11-14 05:18:49.272 main[174436] Value of b is 30
    7 2018-11-14 05:18:49.272 main[174436] Value of b is 20

    Objective-C运算符优先级

    运算符优先级确定表达式中的术语分组。这会影响表达式的计算方式。 某些运算符优先级高于其他运算符; 例如,乘法运算符的优先级高于加法运算符 -

    例如,x = 7 + 3 * 2; 这里,x被赋值为13,而不是20,因为 *运算符的优先级高于+运算符,所以它首先乘以3 * 2然后加上7

    此处,具有最高优先级的运算符显示在下表的顶部,具有最低优先级的运算符显示在下表底部。 在表达式中,将首先评估更高优先级的运算符。

    分类运算符关联性
    后缀 () [] -> . ++ -- 左到右
    一元 + - ! ~ ++ -- (type)* & sizeof 右到左
    相乘 * / % 左到右
    相加 + - 左到右
    位移 << >> 左到右
    关系 < <= > >= 左到右
    相等 == != 左到右
    按位XOR ^ 左到右
    按位OR Ι 左到右
    逻辑AND && 左到右
    逻辑OR ΙΙ 左到右
    条件 ?: 右到左
    分配 = += -= *= /= %= >>= <<= &= ^= Ι= 右到左
    逗号 , 左到右
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  • 原文地址:https://www.cnblogs.com/strengthen/p/10562959.html
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