# #53 – Modulus

August 9, 2010 1 Comment

The **modulus** operator **%**, used as a binary operator

a % b

is defined as the remainder of **a** (dividend) divided by **b **(divisor). Also known as “modulo“.

The idea is to determine the maximum integer that you can multiply **b** by to get a result <=**a. **Let’s call this integer **n**. Then the remainder is just **a – (b * n)**.

Examples:

int n1 = 5 % 2; // 1 [5-(2*2)] int n2 = 39 % 5; // 4 [39-(5*7)] int n3 = 10 % 2; // 0 [10-(2*5)]

If **a **is equal to **b**, the remainder is always 0.

If **a** is less than **b**, the remainder is always equal to **a**.

If either **a** or **b **is negative, the result always matches the sign of **a**.

int n5 = -5 % 2; // -1 int n6 = 5 % -2; // 1 int n7 = -5 % -2; // -1

C# also supports the use of the modulus operator for floating point numbers:

double d1 = 42.5 % 12.2; // ~5.9 [42.5-(12.2*3)]

Great summary, thank you Sean.