string-compress.cpp

#include <iostream>
#include <string>

std::string compress(const std::string &input) {
    auto read_idx = 0, count = 0;
    bool sequence_start = true;
    std::string output;
    while (read_idx < input.size()) {
        char c = input[read_idx];
        if (std::isalpha(static_cast<unsigned char>(c))) {
            if (sequence_start) {
                output.push_back(c);
                read_idx++;
                sequence_start = false;
                count = 1;
            } else {
                if (c != output.back()) {
                    output.append(std::to_string(count));
                    sequence_start = true;
                } else {
                    count++;
                    read_idx++;
                }
            }
        } else {
            throw std::invalid_argument("Invalid character in input string");
        }
    }
    output.append(std::to_string(count));
    if (output.size() > input.size()) {
        throw std::runtime_error("Cannot Compress");
    }
    return output;
}

int main() {
    std::string input;
    while (1) {
        std::cout << "Enter String to compress: ";
        std::getline(std::cin, input);
        try {
            std::string output;
            std::cout << compress(input) << "\n";
        } catch (const std::exception &e) {
            std::cout << "Error: " << e.what() << "\n";
        }
    }
}