OperatorsOnce we know of the existence of variables and constants, we can begin to operate with them. For that purpose, C++ integrates operators. Unlike other languages whose operators are mainly keywords, operators in C++ are mostly made of signs that are not part of the alphabet but are available in all keyboards. This makes C++ code shorter and more international, since it relies less on English words, but requires a little of learning effort in the beginning.You do not have to memorize all the content of this page. Most details are only provided to serve as a later reference in case you need it.Assignment (=)The assignment operator assigns a value to a variable. a = 5;This statement assigns the integer value 5 to the variable a. The part at the left of the assignment operator (=) is known as the lvalue (left value) and the right one as the rvalue (right value). The lvalue has to be a variable whereas the rvalue can be either a constant, a variable, the result of an operation or any combination of these.The most important rule when assigning is the right-to-left rule: The assignment operation always takes place from right to left, and never the other way:a = b;This statement assigns to variable a (the lvalue) the value contained in variable b (the rvalue). The value that was stored until this moment in a is not considered at all in this operation, and in fact that value is lost.Consider also that we are only assigning the value of b to a at the moment of the assignment operation. Therefore a later change of b will not affect the new value of a.For example, let us have a look at the following code - I have included the evolution of the content stored in the variables as comments:// assignment operator#include <iostream>using namespace std;int main (){ int a, b; // a:?, b:? a = 10; // a:10, b:? b = 4; // a:10, b:4 a = b; // a:4, b:4 b = 7; // a:4, b:7 cout << "a:"; cout << a; cout << " b:"; cout << b; return 0;}output:a:4 b:7This code will give us as result that the value contained in a is 4 and the one contained in b is 7. Notice how a was not affected by the final modification of b, even though we declared a = b earlier (that is because of the right-to-left rule).A property that C++ has over other programming languages is that the assignment operation can be used as the rvalue (or part of an rvalue) for another assignment operation. For example:a = 2 + (b = 5);is equivalent to:b = 5;a = 2 + b;that means: first assign 5 to variable b and then assign to a the value 2 plus the result of the previous assignment of b (i.e. 5), leaving a with a final value of 7.The following expression is also valid in C++:a = b = c = 5;It assigns 5 to the all three variables: a, b and c.Arithmetic operators ( +, -, *, /, % )The five arithmetical operations supported by the C++ language are:+ addition- subtraction* multiplication/ division% moduloOperations of addition, subtraction, multiplication and division literally correspond with their respective mathematical operators. The only one that you might not be so used to see is modulo; whose operator is the percentage sign (%). Modulo is the operation that gives the remainder of a division of two values. For example, if we write: a = 11 % 3;the variable a will contain the value 2, since 2 is the remainder from dividing 11 between 3.Compound assignment (+=, -=, *=, /=, %=, >>=, <<=, &=, ^=, |=)When we want to modify the value of a variable by performing an operation on the value currently stored in that variable we can use compound assignment operators:expression is equivalent tovalue += increase; value = value + increase;a -= 5; a = a - 5;a /= b; a = a / b;price *= units + 1; price = price * (units + 1);and the same for all other operators. For example:// compound assignment operators#include <iostream>using namespace std;int main (){ int a, b=3; a = b; a+=2; // equivalent to a=a+2 cout << a; return 0;}output:5Increase and decrease (++, --)Shortening even more some expressions, the increase operator (++) and the decrease operator (--) increase or reduce by one the value stored in a variable. They are equivalent to +=1 and to -=1, respectively. Thus:c++;c+=1;c=c+1;are all equivalent in its functionality: the three of them increase by one the value of c.In the early C compilers, the three previous expressions probably produced different executable code depending on which one was used. Nowadays, this type of code optimization is generally done automatically by the compiler, thus the three expressions should produce exactly the same executable code.A characteristic of this operator is that it can be used both as a prefix and as a suffix. That means that it can be written either before the variable identifier (++a) or after it (a++). Although in simple expressions like a++ or ++a both have exactly the same meaning, in other expressions in which the result of the increase or decrease operation is evaluated as a value in an outer expression they may have an important difference in their meaning: In the case that the increase operator is used as a prefix (++a) the value is increased before the result of the expression is evaluated and therefore the increased value is considered in the outer expression; in case that it is used as a suffix (a++) the value stored in a is increased after being evaluated and therefore the value stored before the increase operation is evaluated in the outer expression. Notice the difference:
