100 C Programming MCQs with Answers and Explanations

C. int main(void) — Hosted main returns int. The void parameter list explicitly specifies no parameters; identifier case matters.

C. Standard I/O declarations — Inclusion supplies header contents during preprocessing. Compilation and linking still have separate jobs.

D. Successful termination — Zero is a success status for hosted termination; returning it does not print a character.

B. ; — A semicolon terminates an expression statement, although not every C construct is an expression statement.

A. .c — The .c extension selects C source by convention. .cpp is C++, .o is an object, and .exe is commonly an executable.

C. // to the end of the line — Line comments beginning // have been part of C since C99. Block comments use slash-star and star-slash.

A. No, C identifiers are case-sensitive — Case is significant in identifiers. Choosing consistent spelling is part of declaring and using the same name.

A. <stddef.h> — stddef.h defines size_t and NULL, along with other common definitions. Some other standard headers also define them.

A. Double quotes — Double quotes delimit a string literal. Single quotes denote character constants, not strings.

D. A newline character — The escape sequence represents a newline in the execution character set. A literal backslash needs its own escape.

D. 1 — sizeof measures C bytes, and char occupies exactly one such byte. CHAR_BIT gives bits per byte.

B. CHAR_BIT from limits.h — CHAR_BIT is at least 8. A C byte is not required to have exactly eight bits on every target.

D. Its range meets the standard minimum, but its width varies — Use limits.h to inspect its range. Hardware and ABI conventions do not create a universal width.

D. It is reduced modulo one more than the maximum value — Unsigned arithmetic is modular. Promotions can change the type in which an expression is evaluated.

B. Undefined behavior — The language does not require wrapping or a diagnostic for an unrepresentable signed arithmetic result.

A. 3 — Both operands are int, so integer division discards the fractional part toward zero.

A. -3 — C17 integer division truncates toward zero when the quotient is representable and the divisor is nonzero.

D. int — Unlike a string literal, an ordinary character constant has type int in C.

A. %zu — The z length modifier with u formats size_t as an unsigned integer. Mismatched variadic argument types are unsafe.

B. If provided, it is an unsigned integer type with exactly 32 bits — Exact-width typedefs are optional when the implementation lacks a type meeting the exact requirements.

D. && — Logical AND evaluates its right operand only when the left operand is nonzero.

C. || — Logical OR does not evaluate the right operand once the left operand has established truth.

A. x == 3 — Double equals compares values; a single equals assigns a value and itself yields a value.

C. do ... while — A do loop checks its condition after its body, unlike while and a conventional for condition.

D. The innermost enclosing loop or switch — break transfers control out of the nearest loop or switch, not arbitrary enclosing blocks.

B. Moves to the iteration expression, then the next condition test — The iteration expression still runs after continue in a for loop, before the condition is checked again.

A. Execution can fall through into the next labeled statements — Case labels do not create implicit breaks. Intentional fallthrough should be clear to readers and tools.

A. Every nonzero value — Scalar conditions test against zero; a negative integer is also true.

B. 7 — Multiplication binds more tightly than addition. Parentheses can explicitly choose another grouping.

A. Exactly one of a() and b(), depending on flag — After evaluating the condition, only the selected second or third operand is evaluated.

C. By value, including pointer values — A pointer argument is also a copied value; writes through it can still modify a caller-owned object.

A. int f(void); — In C17 an empty parameter list in a declaration does not specify a no-argument prototype.

C. It is initialized to zero and retains its value between calls — Static storage duration supplies default zero initialization; block scope remains local.

A. Internal linkage — Internal linkage restricts the name to its translation unit. It does not prohibit calls within that unit.

B. Refer to a compatible external definition supplied elsewhere — Compatible declarations can share an external definition, but extern does not override internal linkage.

D. When execution leaves its associated block — Returning an address of such a local object leaves no live referent after the block is exited.

B. A reachable base case and progress toward it — A base case alone is insufficient if recursive steps never reach it; resource limits still matter.

A. int (*operation)(int, int); — Parentheses bind the pointer declarator to the function type. Without them, the first distractor declares a function returning a pointer.

C. Yes — Returning a struct is standard C and can convey multiple named result fields in one return value.

C. A header included by its callers and definition — A shared header helps keep declaration and definition types consistent across translation units.

B. 4 — Indices begin at zero and end at count minus one. One-past pointers may exist but cannot be dereferenced.

C. Where a is an actual array, not an adjusted function parameter — An array parameter adjusts to a pointer, losing the whole-array size information.

B. It converts to a pointer to its first element — Ordinary array-to-pointer conversion does not supply the length. APIs must carry that information separately.

B. A terminating null character within accessible storage — String functions rely on a reachable terminator. Capacity alone does not make a buffer a valid string.

D. 3 — strlen counts characters before the first null terminator, not the terminator itself.

D. 4 — The array includes c, a, t and the terminating null character; each char occupies one C byte.

A. No, attempting to modify it is undefined behavior — Use a writable array initialized from the literal when you need mutable characters.

C. strcmp — Pointer equality tests addresses, not character sequences. strcmp compares string contents until a difference or terminator.

D. memmove — memmove supports overlap. memcpy requires the source and destination regions not to overlap.

B. Stores that newline in the buffer before the terminator — Successful fgets stores at most size minus one characters and a null terminator; a read newline is retained.

C. A pointer to x — The address-of operator produces a pointer. Not every expression is an addressable object, such as a bit-field.

B. Designates the pointed-to int object — Indirection designates the referent; validity, lifetime and alignment remain preconditions.

C. Use it as an iteration endpoint without dereferencing it — A one-past pointer is permitted for pointer arithmetic and comparisons under the array rules, not as an element.

C. Modifying the int through p — The target is read-only through this pointer. Another valid alias may modify an object that was not defined const.

C. Changing the pointer value p after initialization — The pointer object is const, not the pointed-to int.

D. Initialize those elements and check allocation success — malloc does not initialize the storage’s contents, and a null result must not be dereferenced.

A. All bits are initialized to zero — All-bits-zero is the guarantee, not a universal representation promise for every scalar type.

C. It remains allocated and unchanged — Use a temporary result so failure does not overwrite your only pointer to the still-owned allocation.

C. NULL — free(NULL) has no effect. Invalid non-null pointers and repeated frees can cause undefined behavior.

D. A representability check on the size multiplication — Check count against SIZE_MAX / sizeof *p. Wrapped byte sizes can allocate less storage than later writes require.

B. Padding for alignment — Member and trailing padding depend on the implementation and ABI, so exact layouts need target-specific checks.

D. Members overlap, and the union is large enough for each — Union size can include alignment padding. Track the active variant rather than treating it like a struct.

B. p->member — The arrow form is equivalent to (*p).member when p points to the appropriate struct or union object.

A. A type alias — typedef introduces an alias understood by the compiler; it does not allocate storage or inherently create a distinct type.

D. An argument with side effects may be evaluated more than once — Parenthesizing a macro helps precedence but does not remove repeated evaluation.

D. Prevent repeated processing of the guarded header within one translation unit — An ifndef/define guard prevents repeated declarations from the same header during that preprocessing run.

C. Preprocessing — Preprocessing works on tokens before later translation stages generate the program.

B. An ordinary or static inline function with suitable parameter types — Function arguments are evaluated once per argument occurrence at the call site, avoiding a macro body’s repeated expansion.

A. Its byte offset within the structure — offsetof reports a layout offset. Bit-fields and invalid member designators are not arbitrary safe operands.

D. Padding, widths, byte order and representation can differ — Define an explicit external encoding rather than assuming one target’s in-memory ABI is a portable format.

B. 1 — The return value counts successful conversions, not the input number itself.

D. EOF — EOF indicates input failure before a conversion; a matching failure can instead return zero.

A. To retain the returned character value or EOF indicator — Converting to char too early can conflate an input character with the end-of-file indicator.

B. ferror to distinguish a read error from ordinary end-of-file — An EOF return can accompany a read failure. End-of-file is not the only reason a loop stops.

A. A null pointer — Check the returned FILE pointer before using stream operations.

D. It is truncated — The w mode creates or truncates for writing. Use a suitable mode and error handling to avoid unintended loss.

D. -Wall -Wextra -Wpedantic — These enable useful warning sets. They do not prove correctness or enable every possible warning.

C. It occurs after a successfully built program begins running — Track whether the current source built successfully before diagnosing execution; stale binaries can confuse this distinction.

B. Detecting many invalid memory accesses during execution — A sanitizer is a diagnostic aid. Untested paths and unsupported issue classes still exist.

D. Reject it as a portable prediction — One observed result does not impose a language guarantee on undefined behavior.

A. The array is sorted according to the searched ordering — Sorted order permits eliminating half the interval. Duplicate policies should be documented separately.

C. low + (high - low) / 2 for nonnegative, ordered array-index bounds — With nonnegative ordered array-index bounds of a suitable integer type, the difference fits and the midpoint remains inside the interval. Arbitrary signed bounds need additional range checks.

C. O(n) — An absent target or last-position match can require examining every element once.

C. Shift only when the earlier key is strictly greater — Not moving earlier equal keys past the inserted key preserves the relative order of equal-key records.

B. An early stop after a pass with no swaps — A no-swap pass establishes that the scanned adjacent order is already sorted, giving a linear best case.

B. No, distant swaps can reverse equal-key records — Selecting a minimum and swapping it across equal records can change their original relative order.

A. Take the left-half record first on equal keys — Taking the earlier half’s equal record first preserves original ordering when both halves were stably sorted.

B. Sorted or all-equal input can yield O(n squared) work — Highly unbalanced partitions make the recurrence quadratic. Stack-limiting transformations do not remove that work.

C. O(1) — An in-place heap representation and iterative sift-down use constant auxiliary array storage.

A. (a > b) - (a < b) — Relational results are 0 or 1, so their difference safely gives a negative, zero or positive result.

D. (value & mask) != 0 — Bitwise AND retains shared set bits; comparing with zero then tests whether any remain.

B. value &= ~mask — Complementing the mask creates zeros at selected positions; AND clears those positions.

D. value ^= mask — XOR flips a bit where the mask has 1 and leaves it unchanged where the mask has 0.

B. A negative count or one at least the promoted left operand width — Shift counts are constrained by the promoted operand width. Other signed-operand restrictions can apply too.

B. No — volatile is not mutual exclusion, atomicity or a general synchronization guarantee. Use appropriate atomics or locks.

A. Register side effects and concurrent changes may make read-modify-write invalid — Registers may have write-one-to-clear or other special semantics. Follow the actual device manual.

A. Field encoding and byte order, with explicit width assumptions — Protocols should not inherit padding and machine representation accidentally from an in-memory struct.

C. No, that requires the actual target or a suitable hardware test setup — Host language tests can check pure logic, not establish real peripheral timing or electrical behavior.

C. Failure to make expected progress within a configured time — It requires a meaningful servicing policy; blindly feeding it can hide a stuck application.

D. A bound on elapsed time and a sampling policy that avoids ambiguous wraps — Modular differences are meaningful only under the stated wrap and observation constraints; deadline comparisons may need stricter limits.