Base CS from zero
Values and types: multiple-choice review
Crux Multiple-choice synthesis across the unit: bits carry no meaning, a type is the reading rule, the same bits decode differently, and what type errors actually are.
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You are at middle altitude — in the skySix questions that cut across the whole unit. None of them is a definition to recite. Each asks you to apply the unit’s one idea — bits mean nothing until a type says how to read them — to a concrete situation.
Goal
Confirm you can connect every thread of the unit: a value is raw bits, a type is the rule that interprets them, the same bits decode differently under different rules, and a type system exists to stop the wrong rule from being applied.
Quiz
Completed
A memory cell holds the 8-bit pattern 01000001. Two programs read it: one prints 65, the other prints the letter 'A'. Which statement is correct?
Heads-up Neither value is the byte's 'true' meaning. The pattern 01000001 carries no inherent value. 65 and 'A' are both valid readings of the same bits under two different type rules.
Heads-up Applying a type is a read-only decode. It never alters the stored bits. Both programs read the same unchanged pattern; only their interpretation differed.
Heads-up Bits in a cell carry no permanent type label. The hardware stores eight off/on states. Which type rule to apply is the program's choice, tracked outside the cell.
Quiz
Completed
You must store a value and read it back correctly later. The starting address alone is not enough. What else must the reader know?
Heads-up Memory returns raw bits, never meaning. The hardware knows addresses, not types. Size and interpretation live in the program, not in the cell.
Heads-up Size tells you which bytes to load but not what they mean. Four bytes could be a signed integer, a float, or four characters. Interpretation is a separate, equally necessary piece.
Heads-up A name is a label for the programmer; the machine has discarded it. What is needed at the bit level is size plus interpretation rule — the two halves of a type.
Quiz
Completed
In JavaScript, both 42 and 36.6 report typeof === 'number'. Why is there no separate integer type?
Heads-up JS does not round 36.6 to an integer. It stores the fraction in IEEE 754. Both values are the same type because they share the same 64-bit double format, not because one was rounded away.
Heads-up There is genuinely one number type. typeof reflects reality here: the runtime stores both 42 and 36.6 as doubles. The distinction integer-vs-float is not part of the JS primitive type set at all.
Heads-up JS has a single number type. It does not maintain separate integer and float types under the hood and merge them for display — they are one type, one storage format.
Quiz
Completed
A teammate writes: 'null and undefined are the same thing — both mean empty.' What is the precise correction?
Heads-up They are genuinely distinct values with distinct meanings. null is an intentional 'nothing'; undefined is an unset/missing state the runtime supplies automatically. TypeScript strict mode even tracks them as separate types.
Heads-up Neither is tied to a specific value type. Any variable can be undefined (unassigned) and any slot can be deliberately null. The difference is intentional-vs-automatic absence, not number-vs-object.
Heads-up Garbage collection does not turn one into the other. They are separate primitive values from the start: null is written deliberately, undefined arises from a missing assignment or property.
Quiz
Completed
What is the single underlying problem that every type system — static or dynamic — is built to catch?
Heads-up Memory footprint is a separate concern. A type system tracks which reading rule belongs to which value; it does not exist to limit how many bytes a value uses.
Heads-up Readability is a design and style goal. Type systems target a correctness problem: stopping bits from being decoded with the wrong rule. Clean code and type safety are different layers.
Heads-up Performance is unrelated to the core purpose. The type system's job is to prevent misinterpretation of bits — applying the wrong rule — not to make code faster.
Quiz
Completed
The same type-mismatch bug can be caught at compile time or at run time. What is the practical difference between static (TypeScript) and dynamic (JavaScript) checking?
Heads-up Static typing catches only one class — type mismatches — and even then only before run time. Logic, algorithmic, and business-rule bugs slip past both. Dynamic typing also catches type errors, just later.
Heads-up They target the same underlying problem — bits about to be read with the wrong rule. The difference is timing: compile time versus run time, not the category of error.
Heads-up Run-time detection is late detection: the error surfaces only if and when the line runs, possibly in production. Earlier (static) detection removes the class before shipping, which is why TypeScript exists on top of JS.
Recap
The unit’s spine in one decision chain: a value is a fixed pattern of bits with no inherent meaning; a type supplies the two missing pieces — size and interpretation — that turn bits into a value; the same bits decode to different values under different type rules; JS exposes a small set of primitives (number as one 64-bit IEEE 754 double, string, boolean, and the two distinct absences null and undefined); and a type system exists to stop the wrong rule from being applied — statically before run time, or dynamically at the moment of execution.