Operations on int variables

1 Evaluating integer expressions

A lecture snippet with a mentor as part of the Codegym University course. Sign up for the full course.

The right side of an assignment operator (equal sign) can be any expression — any combination of numbers, variables, and mathematical operators (+, -, *, /).

You can also use parentheses (). In Java, as in mathematics, expressions inside parentheses are evaluated first, and then what is outside the parentheses.

Multiplication and division have equal precedence and are higher than addition and subtraction.

Examples:

int a = (2 + 2) * 2;

int b = (6 - 3) / (9 - 6);

int c = (-2) * (-3);

int d = 3 / 0;

An expression can also include variables:

int a = 1;
int b = 2;
int c = a * b + 2;

What's more, the same variable can be on both the left and the right of the assignment operator:

int x = 5;
x = x + 1;
x = x + 1;
x = x + 1;
x = x + 1;
x = x + 1;

The point here is that in Java the = symbol does not mean equality. Instead, it is an operator that assigns to the variable on the left of the = sign the calculated value of the expression to the right of the = sign.

2 Division of integers

A lecture snippet with a mentor as part of the Codegym University course. Sign up for the full course.

In Java, dividing an integer by an integer always results in an integer. The remainder of the division operation is discarded. Or, you could say that the result of division is always rounded down to the nearest integer.

Examples:

int a = 5 / 2;

int b = 20 / 3;

int c = 6 / 5;

int d = 1 / 2;

3 Remainder of division of integers

Besides addition, subtraction, multiplication, and division of integers, Java also has the modulo operator. It is the percent symbol (%). This operator returns the whole number remainder of dividing an integer by an integer (not the fractional part).

Examples:

int a = 5 % 2;

int b = 20 % 4;

int c = 9 % 5;

int d = 1 % 2;

This is a very useful operator. It is used a lot. For example, to find out whether a number is even or odd, just divide it by 2 and compare the remainder with zero. If the remainder is zero, then the number is even; if it is equal to one, then the number is odd.

Here's what this check looks like:

(a % 2) == 0

where, you guessed it, a % 2 is the remainder of division by 2 (i.e. 0 or 1), and == is used to compare with zero.

4 Increment and decrement

A lecture snippet with a mentor as part of the Codegym University course. Sign up for the full course.

In programming, increasing or decreasing a variable by one are very common operations. There are special commands for these actions in Java:

The increment (increment by one) operator looks like this:

a++;

This statement is exactly the same as a = a + 1; It increases the variable a by one.

The decrement (decrement by one) operator looks like this:

a--;

This statement is exactly the same as a = a - 1; It decreases the variable a by one.

Examples

int x = 5;
x++;
x++;
x++;
x++;
x++;

int x = 5;
x--;
x--;
x--;
x--;
x--;
x--;