Computer Science Notes

Using Input with Scanner & Basic Operators: + - * / %

1. What Is the Scanner Class?

The Scanner class is used in Java to get input from the user through the keyboard. This allows programs to be interactive.

Before using Scanner, it must be imported:

import java.util.Scanner;

2. Creating a Scanner Object

To use the Scanner, we create an object:

Scanner input = new Scanner(System.in);

• Scanner → class name
• input → object name (you can name it anything)
• System.in → tells Java to read from the keyboard

3. Common Scanner Methods

4. Example: Getting User Input

import java.util.Scanner;

public class InputExample {
    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        System.out.print("Enter your age: ");
        int age = input.nextInt();

        System.out.println("You entered: " + age);
    }
}

This program:

• Asks for user input
• Stores it in a variable
• Displays it back to the user

5. Basic Operators in Java

Java uses standard math operators:

6. What Is the % (Modulus) Operator?

The % operator gives the remainder after division.

Examples:

10 % 3 = 1
8 % 2 = 0
7 % 2 = 1

Common uses:

• Check if a number is even or odd
• Control loops
• Validate input or patterns

7. Using Scanner with Math Operators

import java.util.Scanner;

public class Calculator {
    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);

        System.out.print("Enter first number: ");
        int num1 = input.nextInt();

        System.out.print("Enter second number: ");
        int num2 = input.nextInt();

        System.out.println("Addition: " + (num1 + num2));
        System.out.println("Subtraction: " + (num1 - num2));
        System.out.println("Multiplication: " + (num1 * num2));
        System.out.println("Division: " + (num1 / num2));
        System.out.println("Remainder: " + (num1 % num2));
    }
}

8. Important Rules

Integer Division Rule

5 / 2 = 2   // NOT 2.5

Because both numbers are integers, the decimal part is dropped.

To get a decimal result, use at least one double:

double result = 5.0 / 2;  // result is 2.5

Always close the Scanner when finished:

input.close();

9. Real-World Examples

10. Key Vocabulary

• Scanner – Java tool for reading input from the user.
• Operator – A symbol that performs a calculation, like + or *.
• Variable – A storage location for data with a name and type.
• Modulus (%) – Finds the remainder after division.
• Integer Division – Division with integers that drops the decimal part.