Unit 1.3: Expressions and Output

Scope: CS Awesome 2, Section 1.3

Learning Goals

By the end of this lesson, you should be able to:

1. Produce exact output with print and println.
2. Use literals and escape sequences.
3. Evaluate integer and floating-point expressions.
4. Apply operator precedence.
5. Use division and remainder correctly.

Output Statements

System.out.print("Loading ");
System.out.println("complete");
System.out.println("Next task");

Output:

Loading complete
Next task

print stays on the current line. println prints its value and then moves to a new line. Spaces inside a string literal are part of the output.

Literals and Escape Sequences

A literal is the code representation of a fixed value.

42          // int literal
3.25        // double literal
true        // boolean literal
"station"   // String literal

An escape sequence begins with a backslash and represents a character that is difficult to type directly inside a string.

Escape sequence	Meaning
\n	new line
\"	double quote
\\	backslash

System.out.println("Line 1\nLine 2");
System.out.println("She said, \"Go.\"");
System.out.println("C:\\data\\report.txt");

Arithmetic Expressions

An expression combines values, variables, and operators and evaluates to one value.

Operator	Meaning	Example
+	addition	7 + 2 → 9
-	subtraction	7 - 2 → 5
*	multiplication	7 * 2 → 14
/	division	depends on operand types
%	remainder	7 % 2 → 1

Integer and Double Arithmetic

When both operands are int, the result is an int.

System.out.println(7 / 2); // 3

Integer division discards the fractional part. When at least one operand is double, the result is a double.

System.out.println(7.0 / 2); // 3.5
System.out.println(7 / 2.0); // 3.5

Integer division by zero throws an ArithmeticException at run time. Floating-point division follows different rules, but it is still usually a sign that the input or algorithm should be checked.

Compound Expressions and Precedence

Java groups arithmetic operators in this order:

1. parentheses;
2. multiplication, division, and remainder;
3. addition and subtraction.

Operators at the same level are evaluated from left to right.

System.out.println(4 + 3 * 2);       // 10
System.out.println((4 + 3) * 2);     // 14
System.out.println(20 / 5 * 2);      // 8
System.out.println(20 / (5 * 2));    // 2

Use parentheses to make the intended grouping explicit.

The Remainder Operator

a % b gives the remainder after dividing a by b.

int minutes = 137;
System.out.println(minutes / 60); // 2 whole hours
System.out.println(minutes % 60); // 17 remaining minutes

Common uses include checking divisibility, extracting digits, and converting units.

int number = 583;
int lastDigit = number % 10; // 3

Practice Missions

Mission 1: Exact Output

Write output statements that produce exactly:

Path: C:\missions\alpha
Message: "Proceed"
Status:
READY

Use at least two escape-sequence types.

Mission 2: Expression Trace

Predict the value and type of each expression without running it:

19 / 4
19.0 / 4
2 + 3 * 5
(2 + 3) * 5
29 % 6
18 / 4 * 2.0

Mission 3: Time Converter

Given int totalSeconds = 3672;, calculate and print the whole number of minutes and the remaining seconds. Use / and %.

Mission 4: Fix the Formula

The intended result is the average of three integer scores as a decimal. Explain why this expression loses information, then rewrite it:

(score1 + score2 + score3) / 3

Key Summary

Concept	Core idea
print	Prints without adding a new line.
println	Prints and then starts a new line.
Literal	A fixed value written directly in code.
Escape sequence	Special character notation beginning with \.
Integer division	Discards the fractional part.
Double arithmetic	Occurs when at least one operand is double.
%	Produces the division remainder.
Precedence	Determines how operators are grouped.

Source scope: CS Awesome 2, Unit 1.3