07. More on Operators

Some facts :

printf() returns number of characters printed on screen.

if() could have multiple expressions separated by commas

Short Circuit behaviour of && :

The and operator will not evaluate other expressions if, any expression, that comes first, is evaluates to zero value.

Inside if the expressions are evaluated from left to right.

int main() {
  int num1 = 10;
  int num2 = 20;

  // simple usage of if
  if((num1 != 0) && (num2 != 0))
    printf("Number one and two are non-zero\n");

  // Verification of short behaviour
  // Output : We are inside body of if...
  if(printf("") && printf("Second")){
    printf("\nWe are inside body of if...\n");
  }

  return 0;
}

Short circuit behaviour of || :

The or operator will not evaluate expressions futher, if any expression, that comes first, evaluates to non-zero value.

int main() {
  int num1 = 10;
  int num2 = 20;

  // simple usage of if
  if((num1 != 0) || (num2 != 0))
    printf("Number one and two are non-zero\n");

  // Verification of short behaviour
  // Output : First
  if(printf("First") || printf("Second")){
    printf("\nWe are inside body of if...\n");
  }

  return 0;
}

How operators are evaluated ?

The operators are evaluated based on precedence table.

If you find same operators in a expression then, rule of Associativity is applied.

Example :

int age = 10 + 20 + 30 + 40;

Rule of Precedence and Associativity

Rule of precedence, defines the order, in which OS evaluates operators in an expression.

There is a precedence table for this task.

ANSI has changed precedence table in different versions of C language.

Example:

int age = 10 + 20 - 30 * 40;

Rule of Associativity, defines the direction, in which OS evaluates expression with same operators.

Example:

int age = 10 + 20 + 30 + 40;

Precedence	Operator	Description	Associativity
01	++, --	Postfix	Left to Right
01	()	Function Call	Left to Right
01	[]	Array Subscripting	Left to Right
01	.	Direct Member Access	Left to Right
01	->	Indirect Member Access	Left to Right
01	(type){list}	Compound Literal	Left to Right

Precedence	Operator	Description	Associativity
02	++, --	Postfix	Right to left
02	+, -	Unary plus minus	Right to left
02	!, ~	Logical Not and bitwise not	Right to left
02	(type)	Unary plus minus	Right to left
02	*	Unary plus minus	Right to left
02	&	Unary plus minus	Right to left
02	sizeof	Unary plus minus	Right to left
02	_Alignof	Unary plus minus	Right to left

Precedence	Operator	Description	Associativity
03	*, /, %	Multiplication, division, remainder	Left to Right

Precedence	Operator	Description	Associativity
04	+, -	Addition and Subtraction	Left to Right

Precedence	Operator	Description	Associativity
05	<<, >>	Bitwise left shift and right shift	Left to Right

Precedence	Operator	Description	Associativity
06	<, <=	less than and less than equals	Left to Right
06	>, >=	greater than and greater than equals	Left to Right

Precedence	Operator	Description	Associativity
07	==, !=	Equals and not equals	Left to Right

Precedence	Operator	Description	Associativity
08	&	Bitwise And	Left to Right

Precedence	Operator	Description	Associativity
09	^	Bitwise XOR	Left to Right

Precedence	Operator	Description	Associativity
10			Bitwise OR

Precedence	Operator	Description	Associativity
11	&&	Logical And	Left to Right

Precedence	Operator	Description	Associativity
12

Precedence	Operator	Description	Associativity
13	?:	Ternary	Right to Left

Precedence	Operator	Description	Associativity
14	=	Assignment	Right to Left
14	+=, -=	Assignment by sum and difference	Right to Left
14	*=, /=, %=	Assignment by product quotient remainder	Right to Left
14	<<=, >>=	Assignment by bitwise left shigt and right shift	Right to Left
14	&=, ^=,	=	Assignment by bitwise AND XOR OR

Precedence	Operator	Description	Associativity
15	,	Comma	Left to Right