C++ CoreLesson 33 of 441 min read8 questions

Ternary Operator

The conditional operator — pick a value inline with cond ? a : b.

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Concept core idea Watch out easy to get wrong

Concept

Key concepts

Real name = conditional operator; the only operator with three operands. Syntax: cond ? a : b.
It's an expression (yields a value), not a statement — so it works inline: init a variable, a const, a return, a function argument.
Only the chosen branch is evaluated (safe for guarded access like p ? *p : 0).
Both branches must share a common type; if they differ but convert (int/double) the result is the common type — no common type = error.
Low precedence: wrap it in parentheses with << -> cout << (c ? "a" : "b");.
Nesting/chaining is legal but hurts readability; prefer if/else or switch beyond one condition.

One example that shows the key points

C++

int a = 3, b = 7;
int max     = (a > b) ? a : b;          // expression -> initialize a variable
const int x = (a < b) ? 5 : 15;         // works for a const (one-shot init)

int* p = nullptr;
int y = p ? *p : 0;                      // only the chosen branch runs -> safe

auto v = (a < b) ? 1 : 2.5;             // int -> double: result type is double

std::cout << (a < b ? "yes" : "no");    // parentheses: << binds tighter than ?:

Watch out

Easily confused

ternary vs if/else

Ternary is an expression that yields a value (works inline, can init a const). if/else runs statements and returns nothing.

same type vs common type

Branches don't need the SAME type — they need a COMMON type. int/double -> result is double; int/string-literal -> error.

?: vs << precedence

<< binds tighter than ?:, so wrap the ternary in parentheses inside a cout.

Test yourself

8 questions on this lesson. Write your answers from memory, then compare them with the model answers side by side.

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