How Loops & Conditionals Work — Syntax Cheat Sheet

This is a reference page, not a graded exercise. If you're solid in one language but the interview is in another, this is the syntax that trips people up under pressure — not the algorithm.

For loops

Language	Syntax
Java	for (int i = 0; i < n; i++) { ... }
C#	for (int i = 0; i < n; i++) { ... }
Python	for i in range(n): ... (no C-style for loop at all)
JavaScript / TypeScript	for (let i = 0; i < n; i++) { ... }

Iterating a collection directly

Language	Syntax
Java	for (int x : arr) { ... }
C#	foreach (var x in arr) { ... }
Python	for x in arr: ...
JavaScript / TypeScript	for (const x of arr) { ... } — not for...in, which iterates indices/keys, not values

While loops

Language	Syntax
Java / C# / JavaScript / TypeScript	while (condition) { ... }
Python	while condition: ...

If / else

Language	Syntax
Java / C# / JavaScript / TypeScript	if (cond) { ... } else if (cond2) { ... } else { ... }
Python	if cond:\n ...\nelif cond2:\n ...\nelse:\n ... — elif, not else if

Ternary (conditional expression)

Language	Syntax
Java / C# / JavaScript / TypeScript	cond ? valueIfTrue : valueIfFalse
Python	valueIfTrue if cond else valueIfFalse — order is reversed from the others

Switch / match

Language	Syntax
Java	switch (x) { case 1: ...; break; default: ...; } — falls through without break
C#	switch (x) { case 1: ...; break; default: ...; } — falls through is a compile error unless the case is empty
Python	match x: case 1: ... case _: ... (Python 3.10+) — no fallthrough; older Python has no switch at all, use if/elif chains
JavaScript / TypeScript	switch (x) { case 1: ...; break; default: ...; } — falls through like Java

Loop control

Want to...	Java / C# / JS / TS	Python
Exit the loop entirely	break	break
Skip to the next iteration	continue	continue

The gotcha that costs the most time: forgetting break in a Java/JS switch and silently falling into the next case — this compiles and runs, it just does the wrong thing. And in Python, indentation is the block syntax — a misplaced or missing indent is a syntax error, not just a style nit, and mixing tabs and spaces will crash your program.