C Programming — Data Types & Variables Questions & Answers

Q.1 Easy Data Types & Variables

In C programming, when you declare a variable as 'const int x = 5;', what happens if you try to modify it within the program?

A The compiler will generate a warning but allow modification at runtime

B The compiler will generate a compilation error and prevent modification

C The variable will be modified but will revert to original value after each operation

D The modification will be allowed only in the main() function

Correct Answer: B. The compiler will generate a compilation error and prevent modification

EXPLANATION

The 'const' keyword creates a read-only variable. Once initialized, attempting to modify a const variable results in a compilation error (error: assignment of read-only variable). This is enforced at compile-time, not runtime.

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Q.2 Hard Data Types & Variables

What happens when a volatile variable is declared in a multi-threaded C program?

A It becomes thread-safe automatically

B Compiler won't optimize it away and will fetch value from memory each time

C It can only be accessed by one thread

D It doubles in size for redundancy

Correct Answer: B. Compiler won't optimize it away and will fetch value from memory each time

EXPLANATION

volatile tells compiler not to optimize variable accesses and to fetch fresh value from memory, useful for hardware registers and shared memory, but doesn't guarantee thread-safety without synchronization.

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Q.3 Medium Data Types & Variables

Consider a scenario where you need to store a variable that can hold values up to 10 billion. Which data type is most suitable?

A int

B long int

C long long int

D float

Correct Answer: C. long long int

EXPLANATION

int max is ~2.1 billion, long int varies (may be 32 or 64 bits). long long int guarantees 64 bits with max ~9.2 quintillion, sufficient for 10 billion.

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Q.4 Medium Data Types & Variables

What is the output of:
int arr[3] = {1, 2, 3};
int *p = arr;
printf("%d %d", *p, *(p+2));

A 1 3

B 1 2

C 3 3

D Garbage values

Correct Answer: A. 1 3

EXPLANATION

p points to arr[0] which is 1. p+2 points to arr[2] which is 3. Therefore output is '1 3'.

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Q.5 Medium Data Types & Variables

Which storage class has both 'static' and 'auto' properties in certain contexts?

A register

B extern

C static

D volatile

Correct Answer: A. register

EXPLANATION

register requests compiler to store variable in CPU register for faster access but falls back to memory if unavailable, combining automatic allocation with optimization hints.

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Q.6 Hard Data Types & Variables

What will be the result of the following expression:
float x = 0.1 + 0.2;
if(x == 0.3) printf("Equal"); else printf("Not Equal");

A Equal

B Not Equal

C Undefined behavior

D Compilation error

Correct Answer: B. Not Equal

EXPLANATION

Due to floating-point precision limitations, 0.1 + 0.2 does not exactly equal 0.3 in binary representation. Direct comparison with == fails.

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Q.7 Medium Data Types & Variables

In C, what is the difference between 'int' and 'unsigned int' in terms of range on a 32-bit system?

A unsigned int has double the maximum value

B int ranges from -2^31 to 2^31-1, unsigned int from 0 to 2^32-1

C They have identical ranges

D unsigned int ranges from -2^32 to 2^32

Correct Answer: B. int ranges from -2^31 to 2^31-1, unsigned int from 0 to 2^32-1

EXPLANATION

signed int reserves 1 bit for sign, giving range -2147483648 to 2147483647. unsigned int uses all 32 bits for magnitude, giving 0 to 4294967295.

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Q.8 Medium Data Types & Variables

What is the output of the following code:
int a = 5;
int *p = &a;
int **q = &p;
printf("%d", **q);

A 5

B Address of a

C Address of p

D Compilation error

Correct Answer: A. 5

EXPLANATION

q is a pointer to pointer p. *q dereferences q to get p, and **q dereferences p to get the value of a, which is 5.

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Q.9 Easy Data Types & Variables

Which of the following variable declarations will occupy the LEAST memory?

A unsigned int x;

B float y;

C char z;

D double w;

Correct Answer: C. char z;

EXPLANATION

char data type typically occupies 1 byte, which is the minimum. int is 4 bytes, float is 4 bytes, and double is 8 bytes on most systems.

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Q.10 Easy Data Types & Variables

Which keyword is used to declare a variable that cannot be modified after initialization?

A static

B volatile

C const

D extern

Correct Answer: C. const

EXPLANATION

The 'const' keyword declares a constant variable whose value cannot be modified after initialization. Attempting to modify it results in a compile-time error.

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