C语言运算符

在C语言中，运算符是一个符号，告诉编译器执行特定的数学或逻辑函数，C语言提供丰富的内置运算符，并提供以下类型的运算符 -

• 算术运算符
• 关系运算符
• 逻辑运算符
• 按位运算符
• 赋值运算符
• 其它运算符

在本章中，我们将学习每个运算符的工作方式。打开Visual Studio 2017创建一个Win32 Console Application 项目，名称为：c-operators 。

1.算术运算符

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

创建一个源代码文件：arithmetic_operators.c，如下代码 -

#include <stdio.h>

void main() {

   int a = 21;
   int b = 10;
   int c ;

   c = a + b;
   printf("Line 1 - Value of c is %d\n", c );

   c = a - b;
   printf("Line 2 - Value of c is %d\n", c );

   c = a * b;
   printf("Line 3 - Value of c is %d\n", c );

   c = a / b;
   printf("Line 4 - Value of c is %d\n", c );

   c = a % b;
   printf("Line 5 - Value of c is %d\n", c );

   c = a++; 
   printf("Line 6 - Value of c is %d\n", c );

   c = a--; 
   printf("Line 7 - Value of c is %d\n", c );
}

执行上面示例代码，得到以下结果 -

Line 1 - Value of c is 31
Line 2 - Value of c is 11
Line 3 - Value of c is 210
Line 4 - Value of c is 2
Line 5 - Value of c is 1
Line 6 - Value of c is 21
Line 7 - Value of c is 22
请按任意键继续. . .

2.关系运算符

下表显示了C语言支持的关系运算符。假设变量A=10，变量B=20，则 -

创建一个源代码文件：relational_operators.c，如下代码 -

#include <stdio.h>

main() {

   int a = 21;
   int b = 10;
   int c ;

   if( a == b ) {
      printf("Line 1 - a is equal to b\n" );
   }
   else {
      printf("Line 1 - a is not equal to b\n" );
   }

   if ( a < b ) {
      printf("Line 2 - a is less than b\n" );
   }
   else {
      printf("Line 2 - a is not less than b\n" );
   }

   if ( a > b ) {
      printf("Line 3 - a is greater than b\n" );
   }
   else {
      printf("Line 3 - a is not greater than b\n" );
   }

   /* Lets change value of a and b */
   a = 5;
   b = 20;

   if ( a <= b ) {
      printf("Line 4 - a is either less than or equal to  b\n" );
   }

   if ( b >= a ) {
      printf("Line 5 - b is either greater than  or equal to b\n" );
   }
}

执行上面示例代码，得到以下结果 -

Line 1 - a is not equal to b
Line 2 - a is not less than b
Line 3 - a is greater than b
Line 4 - a is either less than or equal to  b
Line 5 - b is either greater than  or equal to b
请按任意键继续. . .

3.逻辑运算符

下表显示了C语言支持的所有逻辑运算符。 假设变量A=1，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
	称为逻辑或运算符。如果两个操作数中的任何一个非零，则条件成立。	(A B)结果为true
!	称为逻辑非运算符，它用于反转其操作数的逻辑状态。如果条件为真，则逻辑NOT运算符将使其结果为false。

示例：创建一个源文件：logical_operators.c，代码如下 -

#include <stdio.h>

main() {

   int a = 5;
   int b = 20;
   int c ;

   if ( a && b ) {
      printf("Line 1 - Condition is true\n" );
   }

   if ( a || b ) {
      printf("Line 2 - Condition is true\n" );
   }

   /* lets change the value of  a and b */
   a = 0;
   b = 10;

   if ( a && b ) {
      printf("Line 3 - Condition is true\n" );
   }
   else {
      printf("Line 3 - Condition is not true\n" );
   }

   if ( !(a && b) ) {
      printf("Line 4 - Condition is true\n" );
   }

}

执行上面代码，得到以下结果 -

Line 1 - Condition is true
Line 2 - Condition is true
Line 3 - Condition is not true
Line 4 - Condition is true

4.按位运算符

按位运算符对位进行操作，并执行逐位运算。 ＆，|和^的真值表如下 -

假设A = 60，B = 13，二进制格式如下：

A = 0011 1100

B = 0000 1101

-----------------

A&B = 0000 1100

A|B = 0011 1101

A^B = 0011 0001

~A = 1100 0011

下表列出了C语言支持的按位运算符。假设变量A=60，变量B=13，则 -

运算符	描述	示例
&	如果二进制AND运算符存在于两个操作数中，则二进制AND运算符将对结果复制一位。	(A&B)= 12，即0000 1100
	二进制OR运算符如果存在于任一操作数中，则复制一位。	(A B) = 61, 即 0011 1101
^	二进制XOR操作符复制该位，如果它设置在一个操作数中，而不是两者。	(A ^ B) = 49, 即, 0011 0001
~	二进制补码运算符是一元的，具有“翻转”位的作用。	(~A)= -61，即 1100 0011的补码形式。
<<	二进制左移操作符，左操作数值左移由右操作数指定的位数。	A << 2 = 240 即, 1111 0000
>>	二进制右移操作符，左操作数值被右操作数指定的位移动。	A >> 2 = 15 即,0000 1111

示例： 创建一个源代码文件：bitwise_operators.c，代码如下所示 -

#include <stdio.h>

main() {

   unsigned int a = 60;    /* 60 = 0011 1100 */  
   unsigned int b = 13;    /* 13 = 0000 1101 */
   int c = 0;           

   c = a & b;       /* 12 = 0000 1100 */ 
   printf("Line 1 - Value of c is %d\n", c );

   c = a | b;       /* 61 = 0011 1101 */
   printf("Line 2 - Value of c is %d\n", c );

   c = a ^ b;       /* 49 = 0011 0001 */
   printf("Line 3 - Value of c is %d\n", c );

   c = ~a;          /*-61 = 1100 0011 */
   printf("Line 4 - Value of c is %d\n", c );

   c = a << 2;     /* 240 = 1111 0000 */
   printf("Line 5 - Value of c is %d\n", c );

   c = a >> 2;     /* 15 = 0000 1111 */
   printf("Line 6 - Value of c is %d\n", c );
}

执行上面代码，得到以下结果 -

Line 1 - Value of c is 12
Line 2 - Value of c is 61
Line 3 - Value of c is 49
Line 4 - Value of c is -61
Line 5 - Value of c is 240
Line 6 - Value of c is 15
请按任意键继续. . .

5.赋值运算符

下表列出了C语言支持的赋值运算符 -

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，将A + B的值分配给C
+=	相加与赋值运算符。它将右操作数添加到左操作数，并将结果分配给左操作数。	C + = A等价于C = C + A
-=	相减与赋值运算符。它从左操作数中减去右操作数，并将结果分配给左操作数。	C -= A等价于 C = C - A
*=	乘以与赋值运算符。它将右操作数与左操作数相乘，并将结果分配给左操作数。	C * = A等价于C = C * A
/=	除以与赋值运算符。它将左操作数与右操作数分开，并将结果分配给左操作数。	C /= A等价于C = C / A
%=	模数与赋值运算符。它需要使用两个操作数的模数，并将结果分配给左操作数。	C %= A等价于C = C % A
<<=	左移与赋值运算符	C <<= 2等价于C = C << 2
>>=	右移与赋值运算符	C >> = 2等价于C = C >> 2
&=	按位与赋值运算符	C &= 2等价于C = C & 2
^=	按位异或运算符和赋值运算符。	C ^= 2等价于C = C ^ 2
	按位包含OR和赋值运算符。

示例： 创建一个源文件：assignment_operators.c ，其代码如下 -

#include <stdio.h>

void main() {

   int a = 21;
   int c ;

   c =  a;
   printf("Line 1 - =  Operator Example, Value of c = %d\n", c );

   c +=  a;
   printf("Line 2 - += Operator Example, Value of c = %d\n", c );

   c -=  a;
   printf("Line 3 - -= Operator Example, Value of c = %d\n", c );

   c *=  a;
   printf("Line 4 - *= Operator Example, Value of c = %d\n", c );

   c /=  a;
   printf("Line 5 - /= Operator Example, Value of c = %d\n", c );

   c  = 200;
   c %=  a;
   printf("Line 6 - %= Operator Example, Value of c = %d\n", c );

   c <<=  2;
   printf("Line 7 - <<= Operator Example, Value of c = %d\n", c );

   c >>=  2;
   printf("Line 8 - >>= Operator Example, Value of c = %d\n", c );

   c &=  2;
   printf("Line 9 - &= Operator Example, Value of c = %d\n", c );

   c ^=  2;
   printf("Line 10 - ^= Operator Example, Value of c = %d\n", c );

   c |=  2;
   printf("Line 11 - |= Operator Example, Value of c = %d\n", c );

}

执行上面代码，得到以下结果 -

Line 1 - =  Operator Example, Value of c = 21
Line 2 - += Operator Example, Value of c = 42
Line 3 - -= Operator Example, Value of c = 21
Line 4 - *= Operator Example, Value of c = 441
Line 5 - /= Operator Example, Value of c = 21
Line 6 - = Operator Example, Value of c = 11
Line 7 - <<= Operator Example, Value of c = 44
Line 8 - >>= Operator Example, Value of c = 11
Line 9 - &= Operator Example, Value of c = 2
Line 10 - ^= Operator Example, Value of c = 0
Line 11 - |= Operator Example, Value of c = 2
请按任意键继续. . .

6.其他操作符：sizeof和三元运算符

除了上面讨论的运算符，还有一些其他重要的运算符，包括sizeof和? ：也被C语言所支持。

示例： 创建一个源文件：sizeof_operator.c ，其代码如下 -

#include <stdio.h>

void main() {

    int a = 4;
    short b;
    double c;
    int* ptr;

    /* example of sizeof operator */
    printf("Line 1 - Size of variable a = %d\n", sizeof(a));
    printf("Line 2 - Size of variable b = %d\n", sizeof(b));
    printf("Line 3 - Size of variable c= %d\n", sizeof(c));

    /* example of & and * operators */
    ptr = &a;    /* 'ptr' now contains the address of 'a'*/
    printf("value of a is  %d\n", a);
    printf("*ptr is %d.\n", *ptr);

    /* example of ternary operator */
    a = 10;
    b = (a == 1) ? 20 : 30;
    printf("Value of b is %d\n", b);

    b = (a == 10) ? 20 : 30;
    printf("Value of b is %d\n", b);
}

执行上面代码，得到以下结果 -

Line 1 - Size of variable a = 4
Line 2 - Size of variable b = 2
Line 3 - Size of variable c= 8
value of a is  4
*ptr is 4.
Value of b is 30
Value of b is 20
请按任意键继续. . .

7.运算符优先级

运算符优先级决定表达式中术语的分组，并决定如何评估计算表达式。 某些运算符的优先级高于其他运营商; 例如，乘法运算符的优先级高于加法运算符，则先要执行乘法运算符的运算。

让我们通过下面的例子了解优先级：

int value = 10 + 20 * 10;

value变量计算结果为：210，因为*(乘法运算符)的优先级比+(加法运算符)高，所以在+(加法运算符)之前进行求值。

C语言运算符的优先级和关联性如下：

示例： 创建一个源文件：operators_precedence.c ，其代码如下 -

#include <stdio.h>

void main() {

    int a = 20;
    int b = 10;
    int c = 15;
    int d = 5;
    int e;

    e = (a + b) * c / d;      // ( 30 * 15 ) / 5
    printf("Value of (a + b) * c / d is : %d\n", e);

    e = ((a + b) * c) / d;    // (30 * 15 ) / 5
    printf("Value of ((a + b) * c) / d is  : %d\n", e);

    e = (a + b) * (c / d);   // (30) * (15/5)
    printf("Value of (a + b) * (c / d) is  : %d\n", e);

    e = a + (b * c) / d;     //  20 + (150/5)
    printf("Value of a + (b * c) / d is  : %d\n", e);

    return 0;
}

执行上面代码，得到以下结果 -

Value of (a + b) * c / d is : 90
Value of ((a + b) * c) / d is  : 90
Value of (a + b) * (c / d) is  : 90
Value of a + (b * c) / d is  : 50
请按任意键继续. . .