Order of Operations Reference
The following is a list of the C order of operations from highest precedence to lowest.
Operators within the same group have equal precedence and evaluate left-to-right
or right-to-left as indicated.
Left-to-Right
++post increment--post decrement()function call[]array subscripting.structure/union member selection->element selection via pointer
Examples
int x[0];
x[0] = 1;
x[1] = 2;
int * i = x;
int y;
y = *i++ //y is 1 and i points to x[1]
(*i)++ //now x[1] is 3 and i points to x[1]
char x[4]; //4 bytes, one 32-bit word
(uint32_t*)x[0]; //returns a char value 0 to 0xff cast as a pointer
((uint32_t*)x)[0]; //returns an 32-bit word
Right-to-Left
++pre increment--pre decrement+unary plus-unary minus!logical not~bitwise not(<type>)type casting*dereference&address ofsizeof()sizeof type or variable
Examples
struct abc {
int a;
int b;
short c;
};
struct abc x;
struct abc * y = &x;
&x.b
//is the same as
&(x.b)
&y->b;
//is the same as because -> is stronger than &
&(y->b);
(int*)&x[0];
//this is an error -- could use
((int*)&x)[0];
Left-to-Right
*multiplication/division%modulo
Examples
a + b * x + y
//is the same as
a + (b * x) + y
Left-to-Right
+addition-subtraction
Examples
c >> a * b + x * y
//is the same as
c >> ((a * b) + (x * y))
a + b * x + y
//is the same as
a + (b * x) + y
Left-to-Right
>>bitwise shift right<<bitwise shift left
Examples
a + b >> x + y
//is the same as
(a + b) >> (x + y)
Left-to-Right
<less than<=less than or equal to>greater than>=greater than or equal to
if( a < b == x > y ){}
//is equivalent to
if( (a < b) == (x > y)){}
Left-to-Right
!=not equal to==equal to
Left-to-Right
&bitwise and
x & 0x2 == 0
//is equivalent to
x & (0x2 == 0)
//fix it using ()
(x & 0x2) == 0
a + b & 0x02 == x & 0x02 + y
//is the same as -- when in doubt use ()
(a + b) & (0x02 == x) & (0x02 + y)
Left-to-Right
^bitwise xor
Left-to-Right
|bitwise or
Examples
a | b && x | y
//is the same as
(a | b) && (x | y)
Left-to-Right
&&logical and
Examples
a == b && x == y
//is the same as
(a == b) && (x == y)
a && b == x && y
//is the same as
a && (b == x) && y
a && b || x && y
//is the same as
(a && b) || (x && y)
a && b | x && y
//is the same as
a && (b | x) && y
Left-to-Right
||logical or
Examples
a || b && x || y
//is the same as
a || (b && x) || y
Left-to-Right
?: ternary operator
a = x > y ? x : y;
//is the same as
if( x > y ){
a = x;
} else {
a = y;
}
a = x > y ? x >>= z : y;
//is the same as
x >>= z;
if( x > y ){
a = x;
} else {
a = y;
}
Right-to-Left
=assign+=assign sum-=assign difference\*=assign product/=assign quotient%=assign remainder<<=assign shift left>>=assign shift right&=assign and^=assign xor|=assign or
Examples
a = b == c
//is the same as
a = (b == c)
a = b += c
//is the same as (right to left evaluation)
a = (b += c)
//or
b += c;
a = b;
Left-to-Right
,comma (evaluates to the value of the second argument)
Examples
//avoid using comma's as an operator :)