1.9 Control of Flow

Learning Objectives

•Write conditional logic with if/else if/else and switch.
•Choose the right loop (for, while, do-while) for a given task.
•Use break and continue to alter loop execution.

Introduction

Control-flow statements determine which parts of a program execute and how many times. Java provides conditional branching (`if`/`else`, `switch`) and loops (`for`, `while`, `do-while`) to move beyond simple top-to-bottom execution.

Key Concepts

`if`/`else if`/`else` chains test conditions in order, executing the first matching branch.

`switch` compares one value against several constant cases; each case should `break` to avoid falling through.

`for` loops suit a known iteration count; `while` suits an unknown count with a pre-check; `do-while` guarantees at least one execution.

`break` exits a loop entirely; `continue` skips to the next iteration.

Java Syntax

Code Examples

Each condition is checked in order; the first `true` branch runs and the rest are skipped. 84 satisfies `score >= 80` but not `score >= 90`, so it prints B.

The `for` loop runs a known number of times (1 through 3). The `while` loop checks its condition before each iteration and relies on `count++` to eventually make it false.

Common Mistakes

⚠Forgetting `break` in a `switch` case, causing execution to "fall through" into the next case unintentionally.
⚠Using `=` instead of `==` inside a condition (Java's compiler rejects this for non-boolean expressions, but it's still a frequent typo to watch for).
⚠Off-by-one errors in `for` loop bounds, e.g. `i <= array.length` instead of `i < array.length`.

Practice

Practice 1

Programming Exercisemedium

Write a loop that prints the numbers 1 through 10, skipping multiples of 3.

Summary

if/else and switch branch execution; for, while, and do-while repeat it. break and continue give fine-grained control over loop execution.

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