A simple 8086 Assembly language project that simulates a mini operating system utilities menu with three main features: a calculator, string reversal, and file information viewer. Designed for EMU8086.

1. Calculator

   • Supports addition (+), subtraction (-), multiplication (*), and division (/).
   • Handles single and double-digit results.
   • Validates division by zero.

2. Reverse String

   • Prompts the user to input a string (up to 50 characters).
   • Outputs the string in reverse order.

3. File Info

   • Reads a filename from the user.
   • Opens the file and retrieves its size in bytes.
   • Handles file-not-found errors.
   • Works for files up to 65535 bytes.

4. Menu

   • Clear screen on each option.
   • Provides a simple text-based menu for navigation.
   • Exit option to terminate the program.

• Assembly language (8086)
• EMU8086 emulator
• DOS interrupts (int 21h) for input/output and file handling

1. Open EMU8086.
2. Create a new project and paste the assembly code (.asm file).
3. Assemble and run the program.
4. Navigate using the menu:
   • Press 1 for Calculator.
   • Press 2 to Reverse String.
   • Press 3 for File Info.
   • Press 4 to Exit.
5. For file info, ensure the file exists in the MyBuild folder.

• Calculator

  • Uses registers AL, CL, BL for storing operands and operation.
  • Supports two-digit results using basic division/modulus logic.

• Reverse String

  • Uses buffered input (0Ah).
  • Correctly prints characters from the end to the start.

• File Info

  • Zero-terminates the filename buffer before calling DOS 3Dh.
  • Uses DOS function 42h to move the file pointer and get file size.
  • Prints file size using a 16-bit number-to-ASCII routine (print_number16).

• Screen clearing

  • Uses BIOS interrupt 10h / 03h to clear screen before displaying menu.