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 of
  • sizeof() 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 :)
X

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