Java uses the standard mathematical operators for addition (`+`), subtraction (`-`), multiplication (`*`), and division (`/`). Java uses (`==`) to test if the value on the left is equal to the value on the right and (`!=`) to test if two items are not equal. But, the percent sign operator (`%`) is the **modulus** or remainder operator.

Try the following in DrJava’s interaction pane. You can download DrJava for free from http://www.drjava.org. The interaction pane lets you try out Java code without having to declare a class. It also automatically prints the result of a statement when you press enter. What does it print when you type each of the following lines and hit enter?

```
11 % 10
3 % 4
8 % 2
9 % 2
```

The **modulus** operator (`%`) returns the remainder after you divide the first number by the second number. The **modulus** operator has been used quite a bit on the AP CS A exam, so you should be familiar with it.

- Use it to check for odd or even numbers (
num % 2 == 1 is odd and num % 2 == 0 is even). Actually, you can use it to check if any number is evenly divisible by another (num1 % num2 == 0)- Use it to get the last digit from an integer number (
num % 10 = last digit on right). This approach could be used on the free response question Self Divisor (Question 1 from 2007). See http://coweb.cc.gatech.edu/ice-gt/1277 for starter code and testing code.- Use it to get the number of minutes left when you convert to hours (
num % 60). Also whenever you have limited storage and you need to wrap around to the front if the value goes over the limit. See question 3 at http://coweb.cc.gatech.edu/ice-gt/1278.

3-4-1: What is the result of 158 % 10?

3-4-2: What is the result of 3 % 8?

You are also expected to know the double plus operator (`++`) and the double minus operator (`--`). The `++` operator is used to add one to the current value: `x++` is the same as `x = x + 1`. The `--` operator is used to subtract one from the current value: `y--` is the same as `y = y - 1`.
You should know that `x += y` is the same as `x = x + y`, `x -= y` is the same as `x = x - y`, `x *= y` is the same as `x = x * y`, and `x /= y` is the same as `x = x / y`.

3-4-3: What are the values of x, y, and z after the following code executes?

```
int x = 0;
int y = 1;
int z = 2;
x--; // x followed bythe double minus sign
y++;
z+=y;
```