ConsoleApp – Gehtsoft Technical Assessment Report

💻 Project Description

This repository contains a Java console application created for the Gehtsoft Training Program entrance assignment.

The project implements two core functionalities:

1. Caesar Cipher Encryption/Decryption – Supports both Russian (including Cyrillic letters with Ё/ё) and English alphabets. The cipher preserves letter case and leaves non-alphabetic characters unchanged. Decryption can be done with a known shift or by brute-force guessing the shift value with candidate output suggestions.
2. Arithmetic Expression Evaluator – Parses and evaluates mathematical expressions with support for addition, subtraction, multiplication, division, parentheses, and decimal numbers. Includes error handling for invalid expressions and division by zero.

🛠️ Technologies

• Java 17 (standard libraries only)
• Console/terminal input and output
• Modular code with clear separation of concerns (different classes for CaesarCipher and ArithmeticEval)

⚙️ How to Compile and Run

On Windows:

Run the batch script to compile and run the project:

build.bat

On MacOS/Linux

Run the shell script to compile and run the project:

./build.sh

Both scripts automatically create the out directory for compiled classes and execute the main application.

💡 My Approach and Assumptions

• Caesar Cipher: Implemented full support for Russian and English alphabets, including wrap-around and case preservation. For decryption without a known shift, brute-force tries all possible shifts and presents candidates to the user for selection.
• Arithmetic Evaluator: Used tokenization, conversion to Reverse Polish Notation (RPN), and evaluation using a stack. Supports floating-point and negative numbers, as well as proper operator precedence and parentheses.
• Error Handling: Input errors (invalid shift, empty files, invalid expressions) are handled gracefully with user-friendly messages.
• User Interface: Simple console menu guiding the user through available operations with clear prompts and results.

📊 Examples of Usage

Caesar Cipher Encryption

Enter your choice: 1
Read from file? n
Enter input: Hello World
Enter shift value: 3
Result: Khoor Zruog

Caesar Cipher Decryption with shift

Enter your choice: 2
Read from file? y/n: n
Enter input: Khoor Zruog
Do you know the shift value? y/n: y
Enter shift value: 3
Result: Hello World

Caesar Cipher Decryption without shift (brute-force)

Enter your choice: 2
Read from file? y/n: n
Enter input: Khoor Zruog
Do you know the shift value? y/n: n
Possible decryptions:
Shift 0: Khoor Zruog
Shift 1: Jgnnq Yqtnf
Shift 2: Ifmmp Xpsme
Shift 3: Hello World
...
Please enter the correct shift value from above: 3
Decryption mode:
Input: "Khoor Zruog"
Output: "Hello World", shift: 3

Arithmetic Expression Evaluation

Enter your choice: 3
Read from file? y/n: y
Enter path to file: testdata/input_num.txt
Enter input: 2 + 3 * 4
Result: 14

📂 Project Structure

ConsoleApp/

• src/
  • Main.java
  • caesar/
    • CaesarCipher.java
  • arithmetic/
    • ArithmeticEval.java
  • reading/
    • Reading.java
  • testdata/
    • input_eng.txt
    • input_rus.txt
    • input_num.txt
  • out/
  • README.md
  • .gitignore