C++ Operators

An operator is a symbol that works on one or two values. Some operators change a variable in place by using the value it already holds.

Adding and taking one

The ++ operator raises the value by 1. The -- operator then lowers the value by 1.

#include <iostream>

int main() {
  int count = 5;
  count++;
  std::cout << count << std::endl;
  count--;
  std::cout << count << std::endl;
  return 0;
}

Updating in place

The += operator adds 6 to the total. The *= operator then multiplies the total by 3.

#include <iostream>

int main() {
  int total = 4;
  total += 6;
  std::cout << total << std::endl;
  total *= 3;
  std::cout << total << std::endl;
  return 0;
}

The remainder

The % operator gives what a division leaves behind. Ten divided by three leaves a remainder of 1.

#include <iostream>

int main() {
  std::cout << 10 % 3 << std::endl;
  return 0;
}

A score updated in steps

Each step works out a new score from the old one. The plain = sign stores each new value in score.

#include <iostream>

int main() {
  int score = 10;
  score = score + 5;
  std::cout << score << std::endl;
  score = score * 2;
  std::cout << score << std::endl;
  return 0;
}

Example

#include <iostream>

int main() {
  int score = 10;
  score++;
  std::cout << "Score: " << score << std::endl;
  score += 9;
  std::cout << "Score: " << score << std::endl;
  score *= 2;
  std::cout << "Score: " << score << std::endl;
  score--;
  std::cout << "Score: " << score << std::endl;
  return 0;
}

Key points

The ++ operator adds 1 to a variable.
The -- operator takes 1 away from a variable.
The += operator adds a value and stores the result in the same variable.
The *= operator multiplies a variable by a value and stores the result.
The % operator gives the remainder after a division.
A plain = sign stores a new value in a variable.

In this example, score starts at 10. The ++ operator raises it to 11, and += adds 9 to make 20. The *= operator doubles 20 to 40. The -- operator then lowers 40 to 39, and a line prints after each step.

Note

An update operator changes the variable itself, not a copy of it.

Try it Yourself

Edit the code, then press Run.

Running is simulated

#include <iostream>

int main() {
  int score = 10;
  score++;
  std::cout << "Score: " << score << std::endl;
  score += 9;
  std::cout << "Score: " << score << std::endl;
  score *= 2;
  std::cout << "Score: " << score << std::endl;
  score--;
  std::cout << "Score: " << score << std::endl;
  return 0;
}

Exercise

A variable named x holds 5. What does x hold after the line x += 3; runs?

8 3 5 15