2.8. Modulus operator

The modulus operator works on integers and yields the remainder when the first operand is divided by the second. In Python, the modulus operator is a percent sign ( % ). The syntax is the same as for other operators:

quotient = 7 // 3 print(quotient) remainder = 7 % 3 print(remainder)

So 7 divided by 3 is 2 with 1 left over.

The modulus operator turns out to be surprisingly useful. For example, you can check whether one number is divisible by another: if x % y is zero, then x is divisible by y.

You can also extract the right-most digit or digits from a number. For example, x % 10 yields the right-most digit of x (in base 10). Similarly, x % 100 yields the last two digits.

csp-10-2-2: What is the result of 18 % 5?

• 0
• This would be correct if it was 18 % 2, but what is the remainder of 18 divided by 5?
• 1
• This would be correct if it was 18 % 17, since 17 goes into 18 one time and the remainder is 18 - 17 = 1.
• 2
• What is the highest multiple of 5 that is less than or equal to 18? The remainder is 18 - that number.
• 3
• The reminder is 3 since 5 goes into 18 three times (15) and 18 - 15 = 3.

csp-10-2-3: What is the result of 2 % 3?

• 2
• The remainder when a smaller number is divided by a larger number is the smaller number.
• 8
• This would be true if it was 2 raised to the 3rd power, but it is modulus.
• 1
• This would be true if it was 3 % 2.
• 0.66666
• This would be true if it was floating point division, but it is modulus.

csp-10-2-4: Match each expression with the type of division the operator performs. Try out these expressions in terminal or review the operators and operands section.
• 7 / 2
• division
• 90 // 4
• floored division
• 45 % 6
• remainder

csp-10-2-5: What is the result of 25 % 4?

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