On a 16-bit Turbo C (DOS) platform using compiler registers, what will this program print? #include int main() { int fun(); int i; i = fun(); printf("%d ", i); return 0; } int fun() { _AX = 1990; // set return register (Turbo C extension) for int }

Introduction / Context:This question targets legacy 16-bit DOS Turbo C behavior where compiler-provided register variables (such as _AX) can be used to specify a function’s return value directly. It assesses platform-specific calling conventions and how return values are passed.

Given Data / Assumptions:

• Compiler: Turbo C in 16-bit DOS.
• Function prototype: int fun();
• In the definition, _AX = 1990; is used without an explicit return statement.
• On this platform, 16-bit integer return values are delivered in the AX register.

Concept / Approach:Many 16-bit compilers map function return values to specific CPU registers. For an int, Turbo C returns via AX. Writing to _AX (a compiler extension naming the register) before the function exits sets the return value exactly as if the function had executed return 1990;.

Step-by-Step Solution:Call fun().Inside fun, assign _AX = 1990.Function returns; caller receives AX content as the integer result.Prints 1990.

Verification / Alternative check:Replacing _AX = 1990; with return 1990; is portable and yields the same output. The register assignment method is non-portable and specific to Turbo C.

Why Other Options Are Wrong:“Garbage value” or “0” would occur only if the convention were different or the code uninitialized the register, which is not the case here. “No output” is incorrect; printf executes.

Common Pitfalls:Attempting to use _AX on modern compilers where it is undefined; assuming this trick is portable across architectures or compilers.

Final Answer:1990