# C語言運算子

• 算術運算子
• 關係運算子
• 邏輯運算子
• 按位元運算子
• 賦值運算子
• 其它運算子

## 1.算術運算子

+ 將兩個運算元相加 A + B = 30
- 從第一個運算元減去第二個運算元 A ? B = -10
* 將兩個運算元相乘 A * B = 200
/ 將第一個運算元除以第二個運算元
% 模數運算子和整數除法後的餘數。 B % A = 0
++ 遞增運算子將整數值增加1 A++ = 11
-- 遞減運算子將整數值減1。 A-- = 9

#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 );
}

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

## 2.關係運算子

== 檢查兩個運算元的值是否相等。 如果相等，則條件成立。 (A == B)結果為false
!= 檢查兩個運算元的值是否相等。 如果值不相等，則條件成立。 (A != B) 結果為true
> 檢查左運算元的值是否大於右運算元的值。 如果是，則條件成立。 (A > B) 結果為false
< 檢查左運算元的值是否小於右運算元的值。 如果是，則條件成立。 (A < B)結果為true
>= 檢查左運算元的值是否大於等於右運算元的值。 如果是，則條件成立。 (A >= B) 結果為false
<= 檢查左運算元的值是否小於等於右運算元的值。 如果是，則條件成立。 (A <= B)結果為true

#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" );
}
}

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

## 3.邏輯運算子

&& 邏輯與運算子。 如果兩個運算元都不為零，則條件成立。 (A && B)結果為false

! 稱為邏輯非運算子，它用於反轉其運算元的邏輯狀態。如果條件為真，則邏輯NOT運算子將使其結果為false

#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" );
}

}

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

## 4.按位元運算子

p q p & q p/q p ^ q
0 0 0 0 0
0 1 0 1 1
1 1 1 1 0
1 0 0 1 1

A = 0011 1100

B = 0000 1101

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

A&B = 0000 1100

A|B = 0011 1101

A^B = 0011 0001

~A = 1100 0011

& 如果二進位制AND運算子存在於兩個運算元中，則二進位制AND運算子將對結果複製一位。 (A&B)= 12，即0000 1100

^ 二進位制XOR操作符複製該位，如果它設定在一個運算元中，而不是兩者。 (A ^ B) = 49, 即, 0011 0001
~ 二進位制二補數運算子是一元的，具有「翻轉」位的作用。 (~A)= -61，即 1100 0011的二補數形式。
<< 二進位制左移操作符，左運算元值左移由右運算元指定的位數。 A << 2 = 240 即, 1111 0000
>> 二進位制右移操作符，左運算元值被右運算元指定的位移動。 A >> 2 = 15 即,0000 1111

#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 );
}

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

## 5.賦值運算子

= 簡單賦值運算子，將右側運算元的值分配給左側運算元 C = A + B，將A + B的值分配給C
+= 相加與賦值運算子。它將右運算元新增到左運算元，並將結果分配給左運算元。 C + = A等價於C = C + A
-= 相減與賦值運算子。它從左運算元中減去右運算元，並將結果分配給左運算元。 C -= A等價於 C = C - A
*= 乘以與賦值運算子。它將右運算元與左運算元相乘，並將結果分配給左運算元。 C * = A等價於C = C * A
/= 除以與賦值運算子。它將左運算元與右運算元分開，並將結果分配給左運算元。 C /= A等價於C = C / A
%= 模數與賦值運算子。它需要使用兩個運算元的模數，並將結果分配給左運算元。 C %= A等價於C = C % A
<<= 左移與賦值運算子 C <<= 2等價於C = C << 2
>>= 右移與賦值運算子 C >> = 2等價於C = C >> 2
&= 按位元與賦值運算子 C &= 2等價於C = C & 2
^= 按位元互斥或運算子和賦值運算子。 C ^= 2等價於C = C ^ 2

#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 );

}

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

## 6.其他操作符：sizeof和三元運算子

sizeof() 返回變數的大小 sizeof(a)，其中a為整數，將返回4
& 返回變數的地址 &a; 返回變數的實際地址。
* 指向變數的指標 *a;
? : 條件表示式 如果條件是真的？ 那麼返回值X：否則返回Y

#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);
}

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

## 7.運算子優先順序

int value = 10 + 20 * 10;

value變數計算結果為：210，因為*(乘法運算子)的優先順序比+(加法運算子)高，所以在+(加法運算子)之前進行求值。

C語言運算子的優先順序和關聯性如下：

#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;
}

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