switch)¶

Month 1 · Week 1 · ⬅ Day 003 · Day 005 ➡ · Journal index

🎯 Learning Objective¶

Use Go's three control structures fluently and solve FizzBuzz cleanly.

📚 Topics¶

if with init statement · for (the only loop) · switch (no fall-through)

📖 Reading / Sources¶

Learning Go ch.4
Tour of Go — Flow control

📝 Notes¶

for is the only loop keyword. Forms: classic for i:=0; i<n; i++, while-style for cond {}, infinite for {}, and for range.
if can carry an init statement: if v := f(); v > 0 { … } — v is scoped to the if/else. Keeps scope tight.
switch has no implicit fall-through (the opposite of C). Cases break automatically; use fallthrough rarely. A bare switch {} with boolean cases is a clean if/else if chain.
Cases can list multiple values: case "Sat", "Sun":.
No parentheses around conditions; braces are mandatory.

💻 Code Examples¶

switch {
case n%15 == 0: return "FizzBuzz"
case n%3 == 0:  return "Fizz"
case n%5 == 0:  return "Buzz"
default:        return strconv.Itoa(n)
}

Full code: examples/control-flow/main.go · FizzBuzz: exercises/.../fizzbuzz

🏋️ Exercises / Practice¶

Exercise	Status	Link
FizzBuzz (1..n) + tests	✅	fizzbuzz
Sum/even-odd with `if` init	✅	examples/control-flow

🐛 Mistakes Made¶

Put the %15 check after %3/%5 first time → numbers like 15 printed "Fizz". Order matters: check the most specific case first.
Reached for a while keyword out of habit — it doesn't exist; for cond {} is the equivalent.

❓ Open Questions¶

When is fallthrough actually useful? (Rare — mostly grouping; multiple values per case is usually better.)

🧠 Active Recall¶

Q: How many loop keywords does Go have, and what are the forms?
A
One: for. Forms — three-part, while-style (for cond), infinite (for {}), and for range.
Q: Does a Go switch fall through by default?
A
No. Each case breaks automatically; opt in with fallthrough.

🪶 Feynman Reflection¶

Go simplifies control flow: one loop keyword for everything, if that can declare a throwaway variable, and a switch that won't surprise you by falling through. FizzBuzz is just "check divisibility, most specific first."

🕳️ Knowledge Gaps¶

for range over channels/maps — comes later (maps Day 011, channels Month 3).

✅ Summary¶

Comfortable with all control flow; FizzBuzz solved and tested.

⏭️ Next Steps / Prep for Tomorrow¶

Day 005: functions, multiple returns, defer, closures.

Time spent	Difficulty	Confidence
90 min	🟦⬜⬜⬜⬜	🟦🟦🟦🟦⬜

Suggested commit: feat(exercises): control flow and FizzBuzz (day 004)