Literals and operators

• Literal / literal constant
  • A fixed value that has been inserted directly into the source code
  • literals have both value and type

# "Hello World" and 5 (not x) are literals
std::count << "Hello World";
int x { 5 };

• Literal vs variable

# literals vs variables
int main()
{
	# 5 is a literal that is printed
	std::cout << 5 << '\n';
 
	# x is a variable that is printed
	int x { 5 };
	std::count << x << '\n';
	
	return 0;
}

• Both output statements do the same thing (print the value 5).
  • literal → the value 5 can be printed directly
  • variable → the value 5 must be fetched from the memory the variable represents

Operators

• operation
  • process involving 0 or more input values (operands) that produces a new value through an operator
• operator
  • +,-,\,*,=,>>,<<,==
  • keywords such as new, delete, throw
  • Most operators in C++ just use their operands to calculate a return value(w/ exceptions such as delete and throw)
  • some has side effects
    • std::cout<<5 has the side effect of printing 5 to console
• arity
  • number of operands that an operator takes as input is called the operator’s arity
  • unary
    • operator- takes operand 5 and outputs -5
  • binary
    • takes operands on left and right
    • for 4+5, operator+ takes 4 and 5
    • << (insertion) and >> (extraction) takes  std::cout or std::cin on the left side, and the value to output or variable to input to on the right side
  • ternary
    • 3 operands
    • conditional operator
  • nullary
    • 0 operands
    • throw
• Advanced stuff
  • For the operators that we call primarily for their return values (e.g. operator+ or operator*), it’s usually obvious what their return values will be (e.g. the sum or product of the operands).
  • For the operators we call primarily for their side effects (e.g. operator= or operator<<), it’s not always obvious what return values they produce (if any). For example, what return value would you expect x = 5 to have?
    • Both operator= and operator<< (when used to output values to the console) return their left operand.
    • Thus, x = 5 returns x, and std::cout << 5 returns std::cout. This is done so that these operators can be chained.
    • For example, x = y = 5 evaluates as x = (y = 5). First y = 5 assigns 5 to y. This operation then returns y, which can then be assigned to x.
    • std::cout << “Hello ” << “world!” evaluates as (std::cout << “Hello ”) << “world!”. This first prints “Hello ” to the console. This operation returns std::cout, which can then be used to print “world!” to the console as well.