# 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

``````