gistfile1.cpp

#include <fstream>
#include <iostream>
#include <locale>
#include <sstream>

class FileModifier
{
    std::string mFilename;

    public:
        FileModifier(const std::string &filename);
        ~FileModifier();
};

FileModifier::FileModifier(const std::string &filename) : mFilename(filename)
{
}

FileModifier::~FileModifier()
{
    std::ifstream in(mFilename.c_str(), std::ios::in);
    std::locale locale("ru_RU.utf-8");
    std::string buffer;

    if(in)
    {
        char tempChar;

        bool isNumber = false;
        bool isFractionDelmiter = false;
        unsigned int fractionLength = 0;

        while(!in.eof())
        {
            in.get(tempChar);

            isFractionDelmiter = (isNumber && (tempChar == ',' || tempChar == '.'));
            isNumber = (tempChar >= 48 && tempChar <= 57) || isFractionDelmiter;

            if(isNumber)
                fractionLength++;

            if(isFractionDelmiter)
                fractionLength = 0;

            if(tempChar != ' ' && (!isNumber || fractionLength < 3))
                buffer += std::toupper(tempChar, locale);
        }

        in.close();

        std::ofstream out(mFilename.c_str(), std::ios::out);
        out << buffer;
        out.close();
    }
    else
        std::cerr << "Input file not found.";
}

int main()
{
    FileModifier("input.txt");
}