CSA Unit 1.3 — Expressions and Output

Learning Objectives

  • 1.3.A: Develop code to generate output and determine the result that would be displayed.
  • 1.3.B: Develop code to utilize string literals and determine the result of using string literals.
  • 1.3.C: Develop code for arithmetic expressions and determine the result of these expressions.

Essential Knowledge

  • 1.3.A.1: System.out.print and System.out.println display information.
    • println → prints + moves to a new line.
    • print → prints but stays on the same line.
    • printf → advanced formatting with placeholders.
  • 1.3.B.1: A literal is a fixed value (like 5, 3.14, or "Hello").
  • 1.3.B.2: A string literal is text inside double quotes.
  • 1.3.B.3: Escape sequences let you control formatting:
    • \" → double quote
    • \\ → backslash
    • \n → newline
    • \t → tab
  • 1.3.C.1: Arithmetic expressions use int and double with operators (+, -, *, /, %).
  • 1.3.C.2: Division with integers truncates toward zero. % gives the remainder.

Expressions in Java

Expressions are combinations of literals, variables, and operators that Java evaluates to produce a value.
In Unit 1.3, we focus on arithmetic expressions.

Arithmetic Operators

  • + → addition
  • - → subtraction
  • * → multiplication
  • / → division
  • % → modulus (remainder)
System.out.println(7 + 3);   // 10
System.out.println(7 - 3);   // 4
System.out.println(7 * 3);   // 21
System.out.println(7 / 3);   // 2  (integer division)
System.out.println(7 % 3);   // 1  (remainder)


### Integer vs. Decimal Division

- If both operands are int, the result is truncated (no decimals).

- If at least one operand is a double, the result is a double.

```java
System.out.println(7 / 3);     // 2
System.out.println(7.0 / 3);   // 2.333333...
System.out.println(7 / 3.0);   // 2.333333...


### Operator Precedence

Java uses order of operations (PEMDAS):

- Parentheses ()

- Multiplication *, Division /, Modulus %

- Addition +, Subtraction -

```java
System.out.println(2 + 3 * 4);   // 14
System.out.println((2 + 3) * 4); // 20


### Combining Strings and Numbers

Using + with a string triggers string concatenation.

```java
System.out.println("Result: " + 5 + 3);   // Result: 53
System.out.println("Result: " + (5 + 3)); // Result: 8




## Outputs

### Types of Output
- **System.out.print()** → prints text without newline.
- **System.out.println()** → prints text with newline.
- **System.out.printf()** → formatted printing (useful for decimals, alignment).

👉 Think of output as the program talking back to the user. Clear formatting is key!


```python
// Example: println vs print
System.out.print("Hello");
System.out.print(" World");
System.out.println("!"); // moves to new line
System.out.println("Done");

Output:

Hello World!
Done

// Example: Escape Sequences
System.out.println("She said: \"Java is fun!\"");
System.out.println("Line1\nLine2");
System.out.println("C:\\Users\\Student");
System.out.println("Column1\tColumn2");

Output:

She said: "Java is fun!"
Line1
Line2
C:\Users\Student
Column1    Column2

Popcorn Hack 1




// Example: Arithmetic Expressions
int a = 7;
int b = 3;
System.out.println("a + b = " + (a + b));
System.out.println("a - b = " + (a - b));
System.out.println("a * b = " + (a * b));
System.out.println("a / b = " + (a / b)); // integer division
System.out.println("a % b = " + (a % b));

double x = 7.0;
double y = 3.0;
System.out.println("x / y = " + (x / y)); // floating-point division

Output:

a + b = 10
a - b = 4
a * b = 21
a / b = 2
a % b = 1
x / y = 2.3333333333333335

Real-World Example — Menu.java

Menus use expressions and output to guide the user. This is a real-world example of combining literals, escape sequences, and arithmetic into meaningful display.

  • Output gives users choices.
  • Expressions let us count and customize menus.
  • Input (preview of Unit 1.4) lets users interact with the program.
import java.util.Scanner;

public class Menu {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        System.out.println("==== Main Menu ====");
        System.out.println("1. Start Game");
        System.out.println("2. Instructions");
        System.out.println("3. Exit");

        System.out.print("Choose an option: ");
        int choice = sc.nextInt();

        System.out.println("You selected option: " + choice);

        int optionCount = 3;
        System.out.println("There are " + optionCount + " total options.");
    }
}

Popcorn Hack 2




Why Menu.java Matters

  • Uses output to display instructions.
  • Uses expressions to dynamically show option count.
  • Uses escape sequences for clean formatting.
  • Real-world: menus are everywhere (ATMs, games, apps, vending machines).

Homework Hack 1

  1. Predict Output: What will this print? 
    System.out.print("AP ");
System.out.println("CSA");
System.out.println("Rocks!");
  2. Fix the Bug: The following is supposed to print C:\Users\Student, but it fails. Correct it: 
    System.out.println("C:\Users\Student");

  3. Menu Hack: Add a 4th option (Settings) to Menu.java and update optionCount accordingly.

  4. Challenge: Use System.out.printf to print pi with 2 decimals. 
    System.out.printf("Pi = %.2f\n", Math.PI);

Homework Hack 2

  • Expand Menu.java into a calculator menu:
    1. Print a menu with options: Add, Subtract, Multiply, Divide.
    2. Ask the user for two numbers.
    3. Use arithmetic expressions to compute and display the result.
    4. Example run: ``` ==== Calculator Menu ====
      1. Add
      2. Subtract
      3. Multiply
      4. Divide Choose an option: 1 Enter first number: 10 Enter second number: 5 Result: 15 ```

Key Takeaways

  • Output = communication from program to user.
  • print vs println vs printf control formatting.
  • Escape sequences handle special characters and formatting.
  • Arithmetic expressions make output dynamic.
  • Menu.java demonstrates real-world application of expressions + output.