C questions in placement tests and university exams are rarely about syntax alone. Most of what you will find here is output prediction, pointer arithmetic, arrays and strings, structures and unions, storage classes, recursion, and file handling. The explanations walk through memory behaviour step by step, which is usually where the confusion sits rather than in the code itself.
What will be the output of: int x = 10; printf("%d %d", x, x++);
Answer: D
int x = 10;
printf("%d %d", x, x++);
Why?
In the same expression, x is:
Read as x
Modified by x++
The order in which function arguments are evaluated is not specified in C. Therefore, the program has undefined behavior.
✅ Correct answer: Undefined Behavior
This is a common C interview/exam trick.
Q.2Hard
Consider the expression: int arr[5]; What does arr represent without the index?
Answer: B
In C, the array name arr (without index) decays to a pointer to its first element, representing the base address.
Q.3Hard
Which storage class has a default value of 0 if not explicitly initialized?
Answer: C
Static variables are initialized to 0 by default. auto and register variables have garbage values if not initialized. extern variables are declared elsewhere.
Q.4Hard
What will be the output of the following code? #include <stdio.h> int main() { int x = 5; printf("%d", ++x + x++); return 0; }
Answer: D
The expression ++x + x++ involves modifying x multiple times without an intervening sequence point, leading to undefined behavior in C.
Q.5Hard
What is the main difference between #define and const in C?
Answer: C
#define is a preprocessor directive replaced before compilation, while const creates an actual variable. const occupies memory; #define does not.
Q.6Hard
Which of the following correctly declares a function pointer?
Answer: B
Function pointers require parentheses around the pointer name: int (*func)(). Option D declares a function returning int pointer, not a function pointer.
Q.7Hard
What will be the output of the following code? #include <stdio.h> int main() { int x = 5; int y = ++x * ++x; printf("%d", y); return 0; }
Answer: C
The expression ++x * ++x modifies x twice without an intervening sequence point, causing undefined behavior.
Q.8Hard
Consider a function declared as 'static int func()'. What is the scope of this function?
Answer: B
When 'static' is applied to a function at file scope, it restricts the function's visibility to that translation unit (file) only.
Q.9Hard
What is the output of: printf("%d", (int)3.7);?
Answer: B
Type casting (int)3.7 truncates the decimal part, converting 3.7 to 3. The fractional part is discarded.
Q.10Hard
Which of the following best describes the 'register' storage class in modern C compilers?
Answer: B
The 'register' keyword is a hint for compiler optimization. Modern compilers often ignore it as they have sophisticated optimization strategies.
Q.11Hard
What will be the output of: int x = 5; printf("%d", x++ + ++x);
Answer: D
This exhibits undefined behavior due to multiple modifications of the same variable 'x' without intervening sequence points.
Q.12Hard
What is the result of: int x = 10; int y = x++ + x++;
Answer: D
Multiple post-increments without sequence points lead to undefined behavior.
Q.13Hard
What is the output of: int x = 5; int y = ++x + x++;
Answer: C
This involves undefined behavior due to modification of x multiple times without intervening sequence points.
Q.14Hard
What is the scope of a variable declared inside a block with 'static'?
Answer: C
A static variable declared in a block has block scope but static storage duration, persisting between function calls.
Q.15Hard
What will be the output of: int a = 1; int b = 2; a = a + b; b = a - b; a = a - b; printf("%d %d", a, b);
Answer: B
Initial: a=1, b=2. After step 1: a=3, b=2. After step 2: a=3, b=1. After step 3: a=2, b=1. Output is '2 1'.
Q.16Hard
Which of the following about function pointers in C is correct?
Answer: B
int (*func)(); declares a pointer to a function that returns int. Option A declares a function returning pointer to int.
Q.17Hard
What is the output of: float x = 25; printf("%f", x);
Answer: B
25 is integer division (not float division), so result is 2 (integer), then converted to 2.0 (float).
Q.18Hard
Which of the following correctly uses memcpy()?
Answer: D
memcpy(dest, src, count) copies 'count' bytes from src to dest. strlen() and sizeof() may not give correct results for all data types.
Q.19Hard
Consider the following declaration: int (*func_ptr)(int, int, int); Which of the following function signatures can be correctly assigned to func_ptr?
Answer: A
func_ptr must point to a function that takes exactly 3 int parameters and returns int. Only option A matches this signature exactly.
