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Calculate Totals and Remainders

Calculate Totals and Remainders

Arithmetic operators add, subtract, multiply and divide values.

A remainder can tell the school how many students remain after forming equally sized teams.

Before this lesson, review Let the Compiler Deduce a Type when needed.

What you’ll learn

  • Use arithmetic operators to calculate Totals and Remainders.
  • Explain how the complete example produces 3 → 2.
  • Make the practice change and explain why the result changes or stays the same.

Follow a complete C++ example

A remainder can tell the school how many students remain after forming equally sized teams.

Read the declarations above main before tracing its statements. Each declared name supplies the value, type or operation used later. The std:: prefix selects a name from the standard library, and cout << sends a value to the output stream.

C++17 · main.cpp · complete program

#include <iostream>

int main()  {
  int students = 11;
  std::cout << students / 3 << '\n' << students % 3 << '\n';
  return 0;
}

Expected output

3
2
Run in C++ compiler →

Connect the code to its result

C++17 · source used in this explanation

#include <iostream>

int main()  {
  int students = 11;
  std::cout << students / 3 << '\n' << students % 3 << '\n';
  return 0;
}

Expected output

3
2

Arithmetic operators add, subtract, multiply and divide values. A remainder can tell the school how many students remain after forming equally sized teams.

Trace the result: Read the complete program below from its starting values to the output operations. Each std::cout statement displays the value supplied at that point; \n begins the next line. The resulting lines, in order, are 3 → 2. In this example, distinguish what the program calculates or changes from what it actually displays.

Important mistakes and boundaries

Integer division discards the fractional part. Division by zero is invalid, and signed integer overflow is not a wrapping guarantee.

Change the school example

C++17 · edit this complete example

#include <iostream>

int main()  {
  int students = 11;
  std::cout << students / 3 << '\n' << students % 3 << '\n';
  return 0;
}

Your task: Use 12 students. Before running your edited program, predict the new output and explain which stored value, condition or object changes. Keep the rest of the example intact.

Use the complete source repeated here; this task does not depend on remembering code from another section.

Worked answer and reasoning

Worked variation: Use 12 students. There are 4 complete teams and remainder 0.

Arithmetic operators add, subtract, multiply and divide values. A remainder can tell the school how many students remain after forming equally sized teams.

Integer division discards the fractional part. Division by zero is invalid, and signed integer overflow is not a wrapping guarantee.

For a baseline run, save this source as main.cpp and use clang++ -std=c++17 -Wall -Wextra -pedantic main.cpp -o school, or equivalent g++ flags. Recompile after editing so that you run the updated executable.

The source and output below belong to the edited program. Compare them with the original example to see the consequence of this single change.

C++17 · worked variation · complete program

#include <iostream>

int main()  {
  int students = 12;
  std::cout << students / 3 << '\n' << students % 3 << '\n';
  return 0;
}

Expected output

4
0
Run in C++ compiler →

Check your understanding

C++17 · original program for this question

#include <iostream>

int main()  {
  int students = 11;
  std::cout << students / 3 << '\n' << students % 3 << '\n';
  return 0;
}
Before making the practice edit, what does the original C++17 program print?
Choose one answer. You can try again.

Answer and explanation

3 2

Arithmetic operators add, subtract, multiply and divide values. A remainder can tell the school how many students remain after forming equally sized teams. Integer division discards the fractional part. Division by zero is invalid, and signed integer overflow is not a wrapping guarantee.

What to remember

Arithmetic operators add, subtract, multiply and divide values. Integer division discards the fractional part. Division by zero is invalid, and signed integer overflow is not a wrapping guarantee.

Useful connections: Let the Compiler Deduce a Type, Give a Task a Name.

Language and design guidance: C++ Core Guidelines and C++ working draft. The draft describes an evolving language; these examples deliberately target C++17.

Reaching the recap and completing the quizzes are separate milestones.

    Next lesson: Combine Conditions →