Consider the following C code: #define clrscr() 100 int main() { clrscr(); printf("%d ", clrscr()); return 0; } What will be the output when this program is executed?

Introduction / Context:
This question focuses on the C preprocessor and how macros are expanded before compilation. The macro clrscr is defined in an unusual way, not as a function that clears the screen but as a constant value. Understanding how the macro expands in both places where it is used explains the final output of the program.

Given Data / Assumptions:

• The macro definition is #define clrscr() 100.
• There is no standard library call named clrscr in this program; clrscr is only the macro.
• The main function calls clrscr with parentheses and then prints the result of clrscr inside printf.

Concept / Approach:
In C, macro definitions are processed by the preprocessor before compilation. The macro clrscr is defined with an empty parameter list and a replacement text of 100. Whenever the preprocessor encounters clrscr() in the code, it replaces that text with 100. The first call clrscr(); becomes simply 100; which is an expression statement that has no effect. The second occurrence, printf("%d", clrscr());, is expanded to printf("%d", 100);. At runtime, the program prints the integer value 100 followed by a newline.

Step-by-Step Solution:
Step 1: Apply macro expansion to clrscr() in the first statement. It becomes 100; which is a valid but useless statement.Step 2: Apply macro expansion to clrscr() inside printf. The call becomes printf("%d", 100);.Step 3: The program now effectively consists of main() { 100; printf("%d", 100); return 0; } after preprocessing.Step 4: When executed, printf prints 100 followed by a newline.Step 5: Therefore, the output observed on the screen is the number 100.

Verification / Alternative check:
If you compile and run the program as given, you will see 100 printed. If you ask the compiler to show the preprocessed output, you can verify that both macro invocations are replaced by 100. This confirms that the macro works as a textual substitution and not as a function call.

Why Other Options Are Wrong:
Option B would be correct only if the macro expanded to zero, which it does not.Option C suggests a compilation error, but the code is valid C and compiles successfully with a standard compiler.Option D claims a runtime exception, but printing an integer constant with printf is safe and does not cause exceptions in normal C environments.

Common Pitfalls:
One pitfall is to assume that clrscr must clear the screen because it is used that way in some older compilers or libraries. In this program, it is purely a macro name and has nothing to do with screen control. Another common confusion is between macros and functions. Macros perform simple textual substitution, so you must mentally expand them to understand the real code that the compiler sees.

Final Answer:
The correct answer is 100.