C++ for Scientists - Technische Universität Dresden

26 CHAPTER 2. C++ BASICS
Operator Action
− subtraction, also unary minus
+ addition
∗ multiplication
/ division
% modulus
−− decrement
++ increment
The modulus operator yields the remainder of the integer division. The ++ operator adds one
to its operand and −− subtracts one. Both can precede or follow the operand. When they
precede the operand, the corresponding operation will be performed before using the operand’s
value to evaluate the rest of the expression. If the operator follows its operand, C ++ will use
the operand’s value before incrementing or decrementing it. Consider the following example:
x = 1;
y = ++x;
x = 1;
z = x++;
As a result of executing these four lines of code, y will be set to 2, x will be set to 2 and z will
be set to 1.
The priority and associativity of binary arithmetic operators is the same as we know it from
math: multiplication and division precedes addition and subtraction. Thus, x + y ∗ z is evaluated
as x + (y ∗ z). Operations of the same priority are left-associative, i.e. x / y ∗ z is
equivalent to (x / y) ∗ z. Unary operators have precedence over binary: x ∗ y++ / −z means
(x ∗ (y++)) / (−z). Nevertheless, as long as you are still learning C ++ and not entirely sure
about the precedences, you might want to add redundant parenthesis instead of wasting hours
debugging your program.
With these operators we can write our first numeric program:
#include
int main ()
{
float r1 = 3.5, r2 = 7.3, pi = 3.14159;
float area1 = pi ∗ r1∗r1;
std::cout ≪ ”A circle of radius ” ≪ r1 ≪ ” has area ”
≪ area1 ≪ ”.” ≪ std::endl;
std::cout ≪ ”The average of ” ≪ r1 ≪ ” and ” ≪ r2 ≪ ” is ”
≪ (r1+r2)/2 ≪ ”.” ≪ std::endl;
return 0 ;
}
2.3.2 Boolean operators
Boolean operators are logical and relational operators. Both return boolean values, therefore
the name. Operators and their significations are: