Modulo operator in C#

TL ; DR:

• The modulo operator (%) calculates the remainder of dividing two values:

  Console.WriteLine(10 % 2); // Output: 0
  Console.WriteLine(15 % 4); // Output: 3
  Console.WriteLine(20 % 3); // Output: 2
  

  
  

• It can also be used with variables:

  int a = 2;
  int b = 4;
  
  Console.WriteLine(b % a); // Output: 0
  Console.WriteLine(11 % b); // Output: 3
  

Full lesson:

Remember how we first learn about the division of two integer numbers in primary school?

The quotient is the number of times a division is completed fully, while the remainder is the amount left that doesn't entirely go into the divisor.

Here are some examples:

10 / 2 = quotient 5, remainder 0
15 / 4 = quotient 3, remainder 3
20 / 3 = quotient 6, remainder 2

The modulo operator:

The modulo operator (%) calculates the remainder of dividing two values:

Console.WriteLine(10 % 2); // Output: 0
Console.WriteLine(15 % 4); // Output: 3
Console.WriteLine(20 % 3); // Output: 2

It can also be used with variables:

int a = 2;
int b = 4;

Console.WriteLine(b % a); // Output: 0
Console.WriteLine(11 % b); // Output: 3

Math.Floor() method

The Math.Floor() method returns the largest integer less than or equal to a given number:

Console.WriteLine(Math.Floor(3.9)); // Output: 3
Console.WriteLine(Math.Floor(5.2)); // Output: 5
Console.WriteLine(Math.Floor(7.0)); // Output: 7

We can use this method if we want to compute the integral part of some division (quotient). It returns a double, so we cast one operand to double before dividing and cast the result back to int:

int a = 2;
int b = 3;

int c = (int)Math.Floor((double)b / a);
Console.WriteLine(c); // Output: 1

When both operands are int, b / a already drops the fractional part, so int c = b / a; gives the same result.

Quotient and remainder:

In programming, we combine both these concepts to get the quotient and remainder of some divison:

// Let's divide 26 by 3:
int quotient = 26 / 3;
int remainder = 26 % 3;

Console.WriteLine(quotient); // Output: 8
Console.WriteLine(remainder); // Output: 2

Assignment
Follow the Coding Tutorial and let's practice with quotient and remainder!

Hint
Look at the examples above if you get stuck.