C++ Operators

Operators let you calculate, compare and combine values in C++.

Arithmetic Operators

Operator	Meaning	Example	Result
`+`	Add	`9 + 2`	`11`
`-`	Subtract	`9 - 2`	`7`
`*`	Multiply	`9 * 2`	`18`
`/`	Divide	`9 / 2`	`4`
`%`	Remainder	`9 % 2`	`1`
`++`	Increase by 1	`x++`
`--`	Decrease by 1	`x--`

Example

cpp

#include <iostream>
using namespace std;

int main() {
  int seconds = 200;
  cout << seconds / 60 << " minutes and " << seconds % 60 << " seconds\n";
  cout << 9 / 2.0 << "\n";
  return 0;
}

Output

3 minutes and 20 seconds
4.5

If both numbers are integers, / gives an integer. Write one as a decimal (2.0) or use static_cast<double> when you need the exact answer.

Prefix and Postfix

x++ uses the value first and then adds 1. ++x adds 1 first and then uses the value:

Example

cpp

#include <iostream>
using namespace std;

int main() {
  int a = 5;
  int b = a++;   // b gets 5, then a becomes 6
  int c = ++a;   // a becomes 7, then c gets 7
  cout << a << " " << b << " " << c << "\n";
  return 0;
}

Output

7 5 7

Assignment Operators

Operator	Same as
`x += 4`	`x = x + 4`
`x -= 4`	`x = x - 4`
`x *= 4`	`x = x * 4`
`x /= 4`	`x = x / 4`
`x %= 4`	`x = x % 4`

Comparison Operators

Each comparison gives a bool result:

Operator	Meaning
`==`	Equal
`!=`	Not equal
`>`, `<`	Greater, less
`>=`, `<=`	Greater or equal, less or equal

Logical Operators

&& and: both must be true
|| or: at least one must be true
! not: reverses true and false

Example

cpp

#include <iostream>
using namespace std;

int main() {
  int marks = 72;
  int attendance = 85;
  bool eligible = marks >= 50 && attendance >= 75;

  cout << boolalpha;
  cout << "Eligible for exam: " << eligible << "\n";
  cout << "Needs help: " << (marks < 40 || attendance < 60) << "\n";
  return 0;
}

Output

Eligible for exam: true
Needs help: false

Order of Operations

*, / and % are done before + and -. Comparisons come after maths, and && comes before ||. When in doubt, use brackets:

Example

cpp

int x = 10 + 2 * 5;     // 20
int y = (10 + 2) * 5;   // 60

Exercise

What is printed by: int n = 3; cout << n++; ?

342An error