This section contains carefully selected MCQs and Previous Year Questions with explanations to help students understand concepts and prepare effectively for examinations, interviews, and competitive tests.
Q: 1What is the value of y after executing the following code?
#define square(p) p*p
void main()
{
int y=square(2+3);
printf("%d",y);
}
Option C
In this program, square(p) is defined as a macro. A macro in C works by simple text substitution, meaning the compiler directly replaces the macro with its definition without adding any extra brackets.
When the statement square(2+3) is written, it is replaced by 2+3*2+3. According to operator precedence rules, multiplication has higher priority than addition, so 3*2 is evaluated first. This makes the expression 2+6+3, which results in the value 11.
Q: 2What is the output of the C code fragment shown below?
#define n 6-4
void main()
{
int i;
i=n*n;
printf(“%d”,i);
}
Option B
In C, macros are expanded textually before compilation. Here, #define n 6-4 means every occurrence of n is replaced by 6-4 without parentheses. So the expression, i = n * n; becomes i = 6-4*6-4;
Now applying operator precedence, the multiplication before subtraction and the expression becomes 6-24-4 = -22
Q: 3What is the output of the following C program?
#include<stdio.h>
#define SQR(x) (x*x)
int main()
{
int a;
int b=4;
a=SQR(b+2);
printf(“%d”,a);
return 0;
}
Option A
In this C program, the macro SQR(x) is defined as (x*x). When a = SQR(b+2) executes with b=4, the preprocessor performs textual substitution, expanding it to a=(b+2*b+2). Following operator precedence, this evaluates as (4+2*4+2) = (4+8+2) = 14, which is then printed.
Q: 4Which keyword is used to define the macros in C/C++?
Option C
In C/C++, macros are defined using the preprocessor directive #define. Preprocessor directives are instructions that are processed before the actual compilation starts.
E.g.:
Here, PI is a macro for a constant value while SQUARE(a) is a macro with arguments.
Q: 5The preprocessors in C are defined with ________________ character.
Option B
In C programming, Preprocessor Directives are lines included in the code that are processed before compilation. These directives always begin with the # (Hash) symbol. Examples of commonly used preprocessor directives starting with # include, #define, #ifdef, #ifndef etc.
| PREPROCESSOR DIRECTIVE | DESCRIPTION |
|---|---|
| #include | Includes standard or user-defined header files in the program. |
| #define | Defines a macro or symbolic constant. |
| #undef | Undefines a previously defined macro. |
| #ifdef | Checks if a macro is defined, includes code if true. |
| #ifndef | Checks if a macro is not defined, includes code if true. |
| #if | Tests a compile-time condition, includes code if true. |
| #else | Specifies alternative code if #if or #ifdef condition is false. |
| #elif | Combines else and if in conditional compilation. |
| #endif | Ends the conditional directive started by #if, #ifdef, #ifndef. |
| #error | Generates a compilation error with a message. |
| #pragma | Provides special instructions to the compiler. |
| #line | Changes the reported line number and filename for errors. |
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