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4.1. The Modulus Operator

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

This program shows the difference between the division operator and the modulus operator.

#include <iostream> using namespace std; int main () { int quotient = 7 / 3; int remainder = 7 % 3; cout << quotient << endl; cout << remainder << endl; return 0; }

The first operator, integer division, yields 2. The second operator yields 1. Thus, 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.

Also, you can use the modulus operator to extract the rightmost digit or digits from a number. For example, x % 10 yields the rightmost digit of x (in base 10). Similarly x % 100 yields the last two digits.

Q-2: How do you know whether the variable x is odd?

• Use x % 2, and if the result is 0, it is odd.
• If you divide a number by two and it has no remainder, that means it is an even number!
• Use x % 2, and if the result is 1, it is odd.
• If you divide a number by two and it has a remainder of one, that means it is an odd number!
• Use x / 2, and if the result is 0, it is odd.
• Dividing a number by two won't give us the information we want.
• Use x / 2, and if the result is 1, it is odd.
• Dividing a number by two won't give us the information we want.

Q-3: Match the modulo expression to its result. Try again!
• 3 % 2
• 1
• 2 % 3
• 2
• 6 % 2
• 0
• 9 % 6
• 3

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