C Language MCQ Questions with Answers

Who created the C programming language at Bell Labs in the early 1970s?

• Dennis Ritchie
• Bjarne Stroustrup
• James Gosling
• Ken Thompson

Answer: Dennis Ritchie. Dennis Ritchie developed C around 1972 from Ken Thompson's B language, to write Unix. Stroustrup later built C++ on top of C, and Gosling created Java.

Which loop always runs its body at least once?

• for
• while
• do-while
• None of them

Answer: do-while. A do-while loop tests its condition after the body, so the body runs once even if the condition is false at the start. for and while test first.

An array is declared as int arr[5];. Which indices are valid?

• 1 to 5
• 0 to 4
• 0 to 5
• 1 to 4

Answer: 0 to 4. C arrays start at index 0, so 5 elements are arr[0] to arr[4]. Reading arr[5] goes past the end, which is undefined behaviour.

Which character marks the end of a string in C?

• '\n'
• '.'
• EOF
• '\0'

Answer: '\0'. A C string is a char array that ends with the null character '\0'. Functions such as strlen and printf stop when they reach it.

What does sizeof(char) always evaluate to in C?

• 1
• 2
• 4
• It depends on the compiler

Answer: 1. The C standard defines sizeof(char) as exactly 1. Other types, such as int and long, vary between systems.

Which printf format specifier prints an unsigned int in hexadecimal?

• %o
• %x
• %d
• %e

Answer: %x. %x prints base 16 with lowercase letters, and %X uses capitals. %o is octal, and %e prints a floating-point number in scientific notation.

What does malloc() return if it cannot allocate the requested memory?

• A block of 0 bytes
• A random address
• NULL
• -1

Answer: NULL. malloc returns a null pointer when it fails, so always check the result before using it. Memory from malloc is released with free().

Which operator accesses a structure member through a pointer to the structure?

• .
• ->
• &
• *

Answer: ->. p->x is shorthand for (*p).x. The dot operator is used on a structure variable itself, not on a pointer to it.

Which storage class lets a local variable keep its value between calls to the same function?

• auto
• register
• extern
• static

Answer: static. A static local variable is initialised once and lives for the whole run of the program, so it remembers its value between calls. An auto variable is created fresh each time.

A global int variable is declared but not initialised. What is its initial value?

• 0
• A garbage value
• -1
• The program will not compile

Answer: 0. Objects with static storage duration, which includes globals, are set to zero before main starts. Uninitialised local (auto) variables are the ones with indeterminate, garbage values.

What does this print? int i = 5; printf("%d", i++);

• 6
• 5
• 4
• It will not compile

Answer: 5. i++ is post-increment: the expression gives the old value, 5, and i becomes 6 afterwards. ++i would print 6.

What does this print? int a = 5, b = 2; float c = a / b; printf("%.1f", c);

• 2.5
• 3.0
• 2.0
• 2

Answer: 2.0. a / b divides two ints, so the result is 2 and the fraction is dropped before the value reaches c. Writing (float)a / b gives 2.5.

What does this print? int x = 0; if (x = 5) printf("yes"); else printf("no");

• no
• Compile error
• Nothing
• yes

Answer: yes. x = 5 is an assignment, not a comparison. Its value is 5, which is non-zero, so the condition is true. Compilers often warn here, because x == 5 was probably meant.

What does this print? int a[] = {10, 20, 30}; int *p = a; printf("%d", *(p + 2));

• 12
• 20
• 30
• An address

Answer: 30. p + 2 moves forward two ints, to a[2], and * reads its value: 30. Pointer arithmetic counts in elements, not bytes.

What does printf("%d", 5 & 3); print?

• 1
• 7
• 6
• 8

Answer: 1. & is bitwise AND: 101 & 011 = 001, which is 1. 5 | 3 would give 7, and 5 ^ 3 would give 6.

What does printf("%zu", sizeof("hello")); print?

• 5
• 8
• 6
• 4

Answer: 6. The string literal "hello" is an array of 6 chars: five letters plus the closing '\0'. strlen("hello") would give 5.

What is the value of b after this code runs? int a = 0, b = 5; if (a && ++b) { }

• 6
• 0
• 1
• 5

Answer: 5. && stops as soon as its left side is false. a is 0, so ++b is never evaluated and b stays 5. This is short-circuit evaluation.

In C99, what is the value of the expression -7 / 2?

• -4
• -3.5
• 3
• -3

Answer: -3. C99 integer division truncates toward zero, so -3.5 becomes -3, and -7 % 2 is -1. Under C89 the rounding direction for negative operands was implementation-defined, so -4 was allowed.

What does this print? #define SQ(x) x * x printf("%d", SQ(2 + 3));

• 25
• 11
• 13
• 10

Answer: 11. A macro pastes text, so SQ(2 + 3) becomes 2 + 3 * 2 + 3, which is 11. Defining it as ((x) * (x)) gives the expected 25.

In C99 (hosted), if int main(void) reaches its closing brace without a return statement, what status does the program return?

• 0
• 1
• A garbage value
• -1

Answer: 0. C99 says reaching the } that ends main returns 0, which means success. In C89 the status was undefined, which is why older code always ends with return 0;.