The Modulo Operator

When you divide $7$ by $3$, you get $2$ with a remainder of $1$. The modulo operator gives you that remainder: $7 \bmod 3 = 1$.

In code, you write this as $7 \% 3$. The $\%$ symbol is the modulo operator in most languages. It shows up everywhere: checking even/odd numbers, cycling through arrays, hashing, and more.

Think of modulo as "what's left over after division." If you have $7$ cookies and give $3$ to each person, you have $1$ cookie left. That's $7 \bmod 3$.