Control Flow

By the end of this lesson you'll be able to make your C++ programs decide what to do — branching with if / else if / else , choosing values with the ternary ?: , matching exact values with switch , and combining conditions with && , || and ! .

Part of the free C++ course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

What You'll Learn

💡 Real-World Analogy

Control flow is the signpost at a fork in the road . Your program walks up to a junction, reads a condition ( "is it raining?" ), and takes the matching path. An if / else if / else chain is a row of signs checked in order — you follow the first one that points your way and ignore the rest. A switch is the departures board at a station: it looks up your exact destination and sends you straight to the right platform. Without these signposts, the program can only ever walk in one straight line.

1. if / else if / else

An if statement runs a block of code only when a condition is true . The condition goes in (parentheses) and must evaluate to true or false . Add else for a fallback, and chain else if for extra options. The chain is checked top to bottom and the first true branch wins — every branch below it is skipped — so put your most specific conditions first. Read this worked example, run it, then you'll write your own.

⚠️ Always use braces { } . Without them, only the single line after the if is conditional — the next line runs every time, which is a classic, silent bug.

2. The Ternary Operator ?:

The ternary is a compact if / else that returns a value . The shape is condition ? valueIfTrue : valueIfFalse . Because it produces a value, you can assign it directly ( string s = ok ? "yes" : "no"; ) or drop it inside a bigger expression. Reach for it on short either/or choices; if a branch needs several statements, a normal if / else reads more clearly.

Your turn. Fill in the two ___ blanks using the hints in the comments, then run it.

3. switch / case / break / default

When you're comparing one value against many exact options , a switch is cleaner than a long else if chain. It works with int , char and enum (not strings or ranges). Each case ends with break to jump out of the switch; default is the catch-all, like else . If you omit break , execution falls through into the next case — handy when you deliberately stack cases ( case 6: case 7: sharing one block), but a bug when you forget it.

Now you try. This vending machine is missing the keyword that stops fall-through and the catch-all label. Fill in the two blanks:

4. Nesting, Logic & if -with-Initializer

Real decisions often depend on several things at once. Combine conditions with the logical operators: && (AND — both must be true), || (OR — either is enough), and ! (NOT — flips true and false). You can also nest an if inside another to make a second decision only when the first passed. Finally, C++17's if -with-initializer lets you declare and test a variable together — if (int x = f(); x > 0) — keeping x scoped to just that if / else .

Common Errors (and the fix)

• Missing break (accidental fall-through): if a case has no break , its code and the next case's both run. Add break; to every case unless you mean to fall through.
• = instead of == : if (x = 5) assigns 5 to x and is always true. Use == to compare; writing if (5 == x) turns the typo into a compile error.
• No default case: if no case matches and there's no default , the switch silently does nothing. Add a default: to catch unexpected values.
• Dangling else: an else binds to the nearest unmatched if , not the one you indented it under. Use braces { } on every nested if so the else pairs with the right one.
• "error: ' x ' was not declared in this scope": a variable from an if -with-initializer or a case block only lives inside that block. Declare it outside if you need it afterwards.

Pro Tips

• 💡 Handle edge cases first: deal with the unusual inputs early with simple if s, then write the normal path without deep nesting.
• 💡 Use switch for menus: it's ideal for processing numbered choices (1, 2, 3…) in a console app.
• 💡 Flatten deep nesting: 4+ levels of indentation is a smell — pull the inner logic into a small function.
• 💡 Scope tightly: prefer if (auto v = lookup(); v) so short-lived variables can't leak into the rest of your function.

📋 Quick Reference

Concept

Syntax

If

if (cond) { ... }

If / else

if (cond) { ... } else { ... }

Else if chain

if (...) {} else if (...) {} else {}

Ternary

result = cond ? a : b;

Switch

switch (x) { case 1: ...; break; default: ...; }

Logical AND / OR / NOT

a && b | a || b | !a

If with initializer (C++17)

if (int x = f(); x > 0) { ... }

Frequently Asked Questions

Mini-Challenge: Ticket Price Calculator

No blanks this time — just a brief and a blank canvas (with an outline to keep you on track). Build it, run it, and check your output against the example in the comments. This combines an if / else if chain with a ternary, exactly like real code.

🎉 Lesson Complete

• ✅ if / else if / else run the first branch whose condition is true
• ✅ The ternary cond ? a : b returns a value you can assign or print
• ✅ switch matches exact int / char / enum values; break stops fall-through; default is the catch-all
• ✅ Combine conditions with && , || and ! , and nest if s for layered decisions
• ✅ if (init; condition) (C++17) scopes a variable to just that test
• ✅ Next lesson: Loops — repeat code efficiently with for , while and do-while

Practice quiz

Continue this course

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• Next: Loops