# C語言運算符

• 算術運算符
• 關係運算符
• 邏輯運算符
• 按位運算符
• 賦值運算符
• 其它運算符

## 1.算術運算符

`+`

`A + B = 30`

`-`

`A − B = -10`

`*`

`A * B = 200`

`/`

`%`

`B % A = 0`

`++`

`A++ = 11`

`--`

`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.關係運算符

`==`

`(A == B)`結果爲`false`

`!=`

`(A != B)` 結果爲`true`

`>`

`(A > B)` 結果爲`false`

`<`

`(A < B)`結果爲`true`

`>=`

`(A >= B)` 結果爲`false`

`<=`

`(A <= B)`結果爲`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.邏輯運算符

`&&`

`(A && B)`結果爲`false`

(A B)結果爲`true`

`!`

``````#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.按位運算符

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``````

`&`

`(A&B)= 12`，即`0000 1100`

(A B) = 61, 即 `0011 1101`

`^`

`(A ^ B) = 49`, 即, `0011 0001`

`~`

`(~A)= -61`，即 `1100 0011`的補碼形式。

`<<`

`A << 2 = 240` 即, `1111 0000`

`>>`

`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.賦值運算符

`=`

`C = A + B`，將`A + B`的值分配給`C`

`+=`

`C + = A`等價於`C = C + A`

`-=`

`C -= A`等價於 `C = C - A`

`*=`

`C * = A`等價於`C = C * A`

`/=`

`C /= A`等價於`C = C / A`

`%=`

`C %= A`等價於`C = C % A`

`<<=`

`C <<= 2`等價於`C = C << 2`

`>>=`

`C >> = 2`等價於`C = C >> 2`

`&=`

`C &= 2`等價於`C = C & 2`

`^=`

`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和三元運算符

`sizeof()`

`sizeof(a)`，其中`a`爲整數，將返回`4`

`&`

`&a;` 返回變量的實際地址。

`*`

`*a;`

`? :`

``````#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.運算符優先級

``int value = 10 + 20 * 10;``

`value`變量計算結果爲：`210`，因爲`*`(乘法運算符)的優先級比`+`(加法運算符)高，所以在`+`(加法運算符)之前進行求值。

C語言運算符的優先級和關聯性如下：

`() [] -> . ++ - -`

`+ - ! ~ ++ - - (type)* & sizeof`

`* / %`

`+ -`

`<< >>`

`< <= > >=`

`== !=`

`&`

`^`

`/`

`&&`

`//`

`?:`

`= += -= *= /= %=>>= <<= &= ^= /=`

`,`

``````#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