Arithmetic Operators

Sooner or later, every program needs to do some math. Just like on paper, C++ gives you five arithmetic operators: addition (+), subtraction (-), multiplication (*), division (/), and modulo (%).

Addition, subtraction, and multiplication

Historically, programming languages use the symbol * for multiplication instead of × since this character isn’t available on a standard keyboard.

The operators +, -, and * behave exactly as you’d expect. Here’s a typical calculation you might write in any real program:

#include <iostream>int main() {    int item_count = 12;    double item_price = 4.99;    double shipping = 3.50;    double subtotal = item_count * item_price;    double total = subtotal + shipping;    double discounted_price = total - 5.00;    std::cout << "Subtotal: " << subtotal << "\n";    std::cout << "Total: " << total << "\n";    std::cout << "After discount: " << discounted_price << "\n";    return 0;}

Terminal

Division and integer truncation

Division in C++ uses the / operator. This is where C++ diverges from what you might expect.

When you divide two int values, the result is also an int. There’s no rounding: the decimal part is simply discarded.

#include <iostream>int main() {    int total_minutes = 130;    int hours = total_minutes / 60;    std::cout << hours << "\n";    return 0;}

Terminal

You’ll see the output 2 and not 2.166....

If you actually need the decimal result, at least one of the two values must be a double (or another floating-point type):

int main() {    int total = 7;    int count = 2;    double average = (double)total / count; // 3.5    std::cout << average << "\n";     return 0;}

Terminal

The (double) cast tells C++ to treat that value as a double for this expression. Once one side of the / is a double, the other side gets promoted to a double automatically, and you get a decimal result.

The modulo operator

The % operator gives you the remainder after integer division. It only works on integers.

#include <iostream>int main() {    int total_minutes = 130;    int hours    = total_minutes / 60;    int leftover = total_minutes % 60;    std::cout << hours << " hours and " << leftover << " minutes\n";    return 0;}

Terminal

You’ll see the output 2 hours and 10 minutes.

The / operator gave us the whole hours; the % operator gave us what was left over. That pair, division and modulo together, is how you split a whole number into parts.

A few other places where % is genuinely useful:

1. Checking parity (even or odd)

You can check whether a number is even or odd by applying modulo 2:

#include <iostream>int main() {    int even_number = 8;    int odd_number = 7;    std::cout << even_number % 2 << "\n"; // 0    std::cout << odd_number % 2 << "\n";  // 1    return 0;}

Terminal

A remainder of 0 means even; 1 means odd.

2. Wrapping around a bigger range to a smaller set

Say you have a fixed set of 7 values and you want to cycle through them repeatedly:

int index = some_number % 7;

This always gives 0–6, no matter how large some_number is.

Operator precedence in arithmetic expressions

Operators like these act on values to form expressions, which C++ evaluates to a single result. C++ evaluates them in the same order you learned in school: multiplication and division before addition and subtraction.

int result = 2 + 3 * 4; // 14, not 20

Multiplication runs first: 3 * 4 = 12, then 2 + 12 = 14.

Similarly, % has the same precedence as multiplication and division:

#include <iostream>int main() {    int result = 2 * 10 + 9 % 4; // 9 % 4 = 1, so 20 + 1 = 21    std::cout << result << "\n";    return 0;}

Terminal

Both * and % are applied before +, giving 21.

Parentheses override the default order:

int result = (2 + 3) * 4; // 20

When in doubt, add parentheses. They make the intent clear and prevent accidents.

Finally, when two operators share the same precedence, C++ evaluates them left to right. This is called left associativity. So 20 % 3 / 2 means (20 % 3) / 2, not 20 % (3 / 2).

Checkpoint

1 / 3

Given this code, what does it print?

int total = 9;
int count = 2;
double result = total / count;
std::cout << result << "\n";

2 / 3

What does the % operator require that / does not?

3 / 3

Given this code, what does it print?

int result = 10 - 12 % 5 / 2;
std::cout << result << "\n";

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Arithmetic Operators

Addition, subtraction, and multiplication

Historically, programming languages use the symbol * for multiplication instead of × since this character isn’t available on a standard keyboard.

The operators +, -, and * behave exactly as you’d expect. Here’s a typical calculation you might write in any real program:

#include <iostream>int main() {    int item_count = 12;    double item_price = 4.99;    double shipping = 3.50;    double subtotal = item_count * item_price;    double total = subtotal + shipping;    double discounted_price = total - 5.00;    std::cout << "Subtotal: " << subtotal << "\n";    std::cout << "Total: " << total << "\n";    std::cout << "After discount: " << discounted_price << "\n";    return 0;}

Terminal

Division and integer truncation

Division in C++ uses the / operator. This is where C++ diverges from what you might expect.

When you divide two int values, the result is also an int. There’s no rounding: the decimal part is simply discarded.

#include <iostream>int main() {    int total_minutes = 130;    int hours = total_minutes / 60;    std::cout << hours << "\n";    return 0;}

Terminal

You’ll see the output 2 and not 2.166....

If you actually need the decimal result, at least one of the two values must be a double (or another floating-point type):

int main() {    int total = 7;    int count = 2;    double average = (double)total / count; // 3.5    std::cout << average << "\n";     return 0;}

Terminal

The modulo operator

The % operator gives you the remainder after integer division. It only works on integers.

#include <iostream>int main() {    int total_minutes = 130;    int hours    = total_minutes / 60;    int leftover = total_minutes % 60;    std::cout << hours << " hours and " << leftover << " minutes\n";    return 0;}

Terminal

You’ll see the output 2 hours and 10 minutes.

The / operator gave us the whole hours; the % operator gave us what was left over. That pair, division and modulo together, is how you split a whole number into parts.

A few other places where % is genuinely useful:

1. Checking parity (even or odd)

You can check whether a number is even or odd by applying modulo 2:

#include <iostream>int main() {    int even_number = 8;    int odd_number = 7;    std::cout << even_number % 2 << "\n"; // 0    std::cout << odd_number % 2 << "\n";  // 1    return 0;}

Terminal

A remainder of 0 means even; 1 means odd.

2. Wrapping around a bigger range to a smaller set

Say you have a fixed set of 7 values and you want to cycle through them repeatedly:

int index = some_number % 7;

This always gives 0–6, no matter how large some_number is.

Operator precedence in arithmetic expressions

int result = 2 + 3 * 4; // 14, not 20

Multiplication runs first: 3 * 4 = 12, then 2 + 12 = 14.

Similarly, % has the same precedence as multiplication and division:

#include <iostream>int main() {    int result = 2 * 10 + 9 % 4; // 9 % 4 = 1, so 20 + 1 = 21    std::cout << result << "\n";    return 0;}

Terminal

Both * and % are applied before +, giving 21.

Parentheses override the default order:

int result = (2 + 3) * 4; // 20

When in doubt, add parentheses. They make the intent clear and prevent accidents.

Finally, when two operators share the same precedence, C++ evaluates them left to right. This is called left associativity. So 20 % 3 / 2 means (20 % 3) / 2, not 20 % (3 / 2).

Checkpoint

1 / 3

Given this code, what does it print?

int total = 9;
int count = 2;
double result = total / count;
std::cout << result << "\n";

2 / 3

What does the % operator require that / does not?

3 / 3

Given this code, what does it print?

int result = 10 - 12 % 5 / 2;
std::cout << result << "\n";

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