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 is the token pasting operator (##) used for in C preprocessor?
Answer: B
The ## operator (token pasting) concatenates two tokens into a single token during preprocessing. For example, #define CONCAT(a,b) a##b creates CONCAT(var,1) as var1.
Q.462Medium
Which of the following macro definitions will correctly compute the absolute value? #define ABS(x) ((x)<0?-(x):(x))
Answer: A
The macro correctly uses the ternary operator with proper parenthesization. Each use of x is wrapped in parentheses to prevent precedence issues. This is a well-formed macro for computing absolute value.
Q.463Medium
What will be the result of this code? #define MAX(a,b) (a>b?a:b) int x = MAX(MAX(2,5), MAX(3,4));
Answer: A
Inner MAX calls: MAX(2,5)=5 and MAX(3,4)=4. Outer MAX call: MAX(5,4)=5. The macro correctly handles nested calls due to proper parenthesization.
Q.464Medium
What will happen when this code is compiled? #define SIZE 10 int arr[SIZE]; #undef SIZE int arr2[SIZE];
Answer: A
After #undef SIZE, the macro SIZE is no longer defined. Attempting to use SIZE in int arr2[SIZE] will cause a compilation error because SIZE is not recognized by the compiler.
Q.465Medium
What is the purpose of predefined macros like __LINE__ and __FILE__?
Answer: B
__LINE__ expands to the current line number and __FILE__ expands to the current filename. These are predefined macros that provide compile-time information useful for debugging and error reporting.
Q.466Medium
What is the output of: #define SQUARE(x) x*x int main() { int a = SQUARE(2+3); printf("%d", a); return 0; }
Answer: B
SQUARE(2+3) expands to 2+3*2+3 = 2+6+3 = 11 due to operator precedence. Proper macro should use parentheses: #define SQUARE(x) ((x)*(x))
Q.467Medium
Which of the following correctly defines a macro with multiple statements?
Answer: C
Option C using do-while(0) is the safest approach to avoid issues with semicolons in if-else statements. Option B can cause problems with control flow statements.
Q.468Medium
What is the output of: #define STR(x) #x int main() { printf("%s", STR(Hello)); return 0; }
Answer: A
The # operator converts the macro argument into a string literal. STR(Hello) becomes "Hello", and printf outputs Hello without quotes.
Q.469Medium
What is the issue with this macro: #define MAX(a,b) a>b?a:b int x = MAX(2, 3); int y = MAX(++i, ++j);
Answer: B
In MAX(++i, ++j), both i and j are incremented twice due to double evaluation. Parentheses help but don't solve side effects completely.
Q.470Medium
What is the purpose of #pragma pack() directive?
Answer: B
#pragma pack() controls how compiler aligns structure members in memory. #pragma pack(1) minimizes padding, while #pragma pack() without arguments resets to default.
Q.471Medium
What is the output of: #define ADD(x,y) (x+y) int main() { printf("%d", ADD(5,3)*2); return 0; }
Answer: A
ADD(5,3)*2 expands to (5+3)*2 = 8*2 = 16. Parentheses around the entire macro definition protect against precedence issues.
Q.472Medium
What is the output of: #define MIN(a,b) ((a)<(b)?(a):(b)) int main() { printf("%d", MIN(10, 5*2)); return 0; }
Answer: B
MIN(10, 5*2) expands to ((10)<(5*2)?(10):(5*2)) = ((10)<(10)?10:10) = 10. Both values are equal due to evaluation order.
Q.473Medium
Which of the following about preprocessor is TRUE?
Answer: D
Preprocessor is a separate tool that processes directives before actual compilation. It prevents recursive macro expansion to avoid infinite loops.
Q.474Medium
What is the correct way to define a multi-line macro in C?
Answer: B
Backslash (\) at the end of line continues a macro definition to the next line. This is the standard way to create multi-line macros in C.
Q.475Medium
Consider the preprocessor directive #define MAX 100. If this macro is used in multiple source files, which statement is TRUE?
Answer: A
Macros are expanded during preprocessing in each translation unit separately. If #define MAX 100 appears in multiple source files, the constant 100 gets substituted in each file independently, potentially creating code duplication. To avoid this, the macro should be defined in a header file with include guards.
Q.476Medium
What is the output of the following code? #define SQUARE(x) x*x int main() { int a = 5; printf("%d", SQUARE(a+1)); return 0; }
Answer: C
Without parentheses around 'x' in the macro, SQUARE(a+1) expands to a+1*a+1 = 5+1*5+1 = 5+5+1 = 11. The macro should be defined as #define SQUARE(x) ((x)*(x)) to avoid operator precedence issues.
Q.477Medium
What will be the result of executing the following? #define PRINT(x) printf(#x) int main() { int a = 10; PRINT(a); return 0; }
Answer: A
The '#' operator (stringification) converts the macro argument into a string literal. PRINT(a) expands to printf("a"), which prints 'a'. If it were PRINT(10), it would print '10' as a string.
Q.478Medium
What is the purpose of #line directive in C preprocessing?
Answer: B
#line directive changes the line number and filename reported by the compiler in error messages and by __LINE__ and __FILE__ macros. Syntax: #line line_number "filename"
Q.479Medium
Which of the following correctly uses #pragma once for header file protection in 2024 standards?
Answer: B
While #pragma once is technically non-standard, it is supported by virtually all modern compilers (GCC, Clang, MSVC) since 2024. It's simpler than include guards and prevents multiple inclusion more elegantly. Both approaches work, but #pragma once is increasingly preferred.
Q.480Medium
Which preprocessor directive is used to generate a compiler warning or error message at compile time?
Answer: B
#error is standard C and generates a compilation error. #pragma message is commonly supported for warnings. #warn and #warning are non-standard. These are useful for version checking and compile-time notifications.
