Binary Encryption

#include <iostream>
#include <fstream>
#include <string>

int pow(const int &base, const int &index)
{
    if(index == 0)
    {
        return 1;
    }
    else
    {
        int res = 1;
        for(int i = 0; i < index; ++i)
        {
            res *= base;
        }
        return res;
    }
}

int binary_to_decimal(const std::string &invertedBinary)
{
    int convertedDecimal = 0;

    const short ZERO_IN_ASCII = 48;
    const short BASE_OF_BINARY = 2;

    for(int i = 0; i < invertedBinary.size(); ++i)
    {
        int binaryCypher = static_cast<int>(invertedBinary[i]) - ZERO_IN_ASCII;
        convertedDecimal += (binaryCypher * pow(BASE_OF_BINARY,invertedBinary.size()-i-1));
    }
    return convertedDecimal;
}

std::string invert_binary_number(const std::string &binary)
{
    std::string encryptedBinary = "";
    for(int i = 0;  i < binary.size(); ++i)
    {
        if(binary[i] == '0')
        {
            encryptedBinary += '1';
        }
        else if(binary[i] == '1')
        {
            encryptedBinary += '0';
        }
    }
    return encryptedBinary;
}

std::string decimal_to_binary(int dec)
{
    std::string unreversedConvertedBinary = "";
    while(dec > 0)
    {
        unreversedConvertedBinary += std::to_string(dec%2);
        dec /= 2;
    }
    for(int i = 0; i < unreversedConvertedBinary.size()/2; ++i)
    {
        int j = unreversedConvertedBinary.size() - i -1;
        int temp = unreversedConvertedBinary[i];
        unreversedConvertedBinary[i] = unreversedConvertedBinary[j];
        unreversedConvertedBinary[j] = temp;
    }
    return unreversedConvertedBinary;
}

std::string encode(const std::string &input)
{
    std::string addToResult = "";
    for(int i = 0; i < input.size(); ++i)
    {
        addToResult += static_cast<char>(binary_to_decimal
                                                (invert_binary_number
                                                    (decimal_to_binary(static_cast<int>(input[i])))));
    }
    return addToResult;
}

int main()
{
    std::fstream file ("input.txt", std::fstream::in);
    std::fstream output("output.txt", std::fstream::out|std::fstream::trunc);
    std::string input;
    while(getline(file,input))
    {
        output<<encode(input);
    }
    file.close();
    output.close();
    return 0;
}