DOS Calculator Program

A vintage DOS calculator application written in C that provides basic arithmetic operations through a colorful windowed text interface. Features file operations, directory browsing, and string manipulation capabilities typical of classic DOS applications.

What it does (high level)

This calculator program provides:

• Basic arithmetic operations: Addition, subtraction, multiplication, and division
• String manipulation: Input and reverse strings with character analysis
• File operations: Save calculations and results to data files
• Directory browser: Navigate file system and manage data files
• Interactive interface: Color-coded windows with keyboard navigation
• Drive detection: Automatically detects available disk drives
• Error handling: Prevents division by zero and validates input

The program runs in a continuous loop, waiting for user input through keyboard commands and providing immediate visual feedback through its windowed interface.

Requirements

Development Tools

C Compiler:

• Borland Turbo C/C++ for DOS (recommended versions 3.0-3.1)
• Borland C++ 3.1 or compatible DOS C compiler

Required Headers:

• Standard C libraries (stdio.h, string.h, math.h, ctype.h)
• DOS-specific headers (dos.h, dir.h, mem.h)
• Borland-specific console library (conio.h)

Runtime Environment

• DOSBox (recommended) - for modern systems
• FreeDOS or MS-DOS - on real hardware or VM
• Standard 80×25 text mode console
• At least 640KB conventional memory

System Requirements

• 16-bit DOS environment (real or emulated)
• VGA or compatible text display for colors
• Keyboard input support
• File system access for data storage

Quick Setup with DOSBox

1. Prepare development environment:

   C:\dos\
   ├── bin\          (Turbo C compiler files: TC.EXE, TCC.EXE, etc.)
   ├── include\      (C header files)
   ├── lib\          (C library files)
   └── src\          (calculator.c source file)
   

2. Launch DOSBox and mount:

   mount c c:\dos
   c:
   set path=c:\bin

3. Compile the program:

   cd \src
   tcc -ms -Ic:\include -Lc:\lib calculator.c

   This creates CALCULATOR.EXE

4. Run the calculator:

   calculator

Program Controls

Main Operations:

• + - Addition
• - - Subtraction
• * - Multiplication
• / - Division
• m - String input mode
• Home - Information display
• E - Exit program

File Browser:

• Tab/Shift+Tab - Navigate between fields
• Enter - Confirm selection
• Esc - Cancel operation
• Arrow Keys - Navigate file/directory lists

Expected Behavior

When launched, the program will:

• Display a colorful windowed interface
• Show available operations in the status bar
• Wait for user input to perform calculations
• Automatically save results to data files
• Provide file browser for managing saved calculations

Troubleshooting

Build Issues:

• Ensure Turbo C include and library paths are correct
• Use small memory model (-ms) for DOS compatibility
• Verify all required headers are available

Runtime Issues:

• Colors not displaying: Use DOSBox with VGA text mode support
• File operations failing: Check write permissions and available disk space
• Keyboard input problems: Ensure DOSBox window has focus

DOSBox Configuration:

• Default settings work for most features
• Ensure machine=svga_s3 for proper text colors
• No special CPU or memory configuration needed

Features

Calculator Functions:

• Floating-point arithmetic with 7-digit precision
• Input validation and error checking
• Division by zero protection

File Management:

• Automatic result logging to .DAT files
• Directory browsing and navigation
• Drive detection and switching
• File deletion capabilities

User Interface:

• Color-coded windows and status bars
• Context-sensitive help text
• Keyboard-driven navigation
• Visual feedback for all operations

Educational Value

This program demonstrates:

• Classic DOS C programming techniques
• Borland-specific console functions (conio.h)
• File I/O operations in DOS
• Directory and drive management
• State machine programming patterns
• Text-mode user interface design

Perfect for learning about vintage DOS development, file system programming, and classic user interface design patterns.

License

Educational/demonstration code. Add appropriate license if redistributing.