Switch Statements

Why we need switch

You are building the menu for an ATM: 1 checks the balance, 2 withdraws, 3 deposits, 4 prints a statement, 5 exits.
You could write it as a chain of if and else if. It works.
But look at what you typed: you wrote choice == five separate times. You are asking the same question about the same variable over and over, and the repetition hides the actual point, which is a simple list of options.
switch is built for exactly that shape.

What is a switch?

A switch looks at one value once, then jumps straight to the label that matches it.

switch (value) names the thing being tested. case X: is a label meaning "if the value is X, start here". break means "we are done, leave". default is the catch-all, the else of the switch.

The variable is named a single time at the top, and under it sits a flat list of options anyone can scan in two seconds.

Code

switch (choice) {  case 1:      checkBalance();      break;  case 2:      withdraw();      break;  default:      exit();}

Fall-through, which catches everybody once

Leave out a break and something strange happens.

Here is why. A case is not a container. It is a doorway. The switch jumps in at the matching label and then keeps running straight down through everything below it, ignoring the other labels completely, until it hits a break or reaches the end.

break is not decoration. It is the wall that stops the flow.

Watch out

When you forget it, the bug is quiet. Your program does not crash. It just does extra things, and you will stare at the code for twenty minutes before you see it.

Fall-through on purpose

Once you understand it, it becomes useful. Stack labels with nothing between them to group options:

Code

switch (day) {  case 6:  case 7:      print("Weekend");      break;  default:      print("Weekday");}

Case 6 has no body, so it falls straight into case 7. Both give "Weekend". This is a clean, standard pattern rather than a trick.

What a switch cannot do

This is where beginners get stuck, so be clear about the limits. A switch compares one value against fixed, exact options. That is all.

No ranges. You cannot write case marks > 90.
No conditions. Nothing combined with and or or.
Labels must be constants, known before the program runs. A variable cannot be a label.
Only some types. Integers and characters everywhere, strings in modern Java, C# and JavaScript. Floats almost never, because exact equality on floats is unreliable anyway.

If your decision needs a range or a combined condition, switch is the wrong tool.

	switch	if / else
Good for	One variable, many fixed values	Ranges, and combined conditions
Typical use	Menus, states, commands, weekdays	Anything with a comparison in it
Shape	A flat list, scannable at a glance	A chain, read top to bottom

Rough guide: exact matches on one value go to switch, everything else goes to if / else.

Python does not have one

If Python is your first language this chapter looks like a foreign country, because Python deliberately left switch out. Three things you use instead.

A chain. Perfectly normal and idiomatic: if, elif, else.

A dictionary. When each case just calls a function, this is elegant:

Code

actions = {  1: check_balance,  2: withdraw,  3: deposit,} action = actions.get(choice, exit)   # exit is the defaultaction()

match, from Python 3.10. The closest thing to a switch, and more powerful:

Code

match choice:  case 1:      check_balance()  case 2:      withdraw()  case 6 | 7:      weekend()  case _:      exit()

Two differences from the C-style switch. match has no fall-through, so no break is needed. And case _ is the default.

Newer Java and JavaScript offer an arrow form that removes fall-through entirely and returns a value: case 6, 7 -> "Weekend";. If your language supports it, prefer it. No break, no accidents, and the whole thing produces a value you can assign.

Mistakes to watch for

Watch out

Forgetting break, causing silent fall-through. The number one switch bug by a distance.
Forgetting default, so an unexpected value does nothing at all.
Trying to use a range or a condition in a case label.
Using a variable as a label. Labels must be constants.
Assuming Python has a switch. It has match, and only from 3.10.

Quick recap

switch tests one value against a list of exact options
A case is a doorway, not a box. Execution falls through until a break
default catches everything that matched nothing
Stacked cases with no body are a deliberate way to group options
No ranges, no conditions, no variable labels
Python uses a chain, a dictionary, or match

A case is a doorway into the switch, and break is the only thing that stops you walking through the rest of the house.