/* * Date: 01/04/19 * Author: G.T.T * * This code features the baseToDecimal function (and its helpers) which will * be part of my NumberSystems class. In my old code I used expanded notation, * where digits are multiplied by their place values & summed in order to * perform base-to-decimal conversion. However, this program shows an alternate * method which I used to obtain the same results. * * Web search topics: * - Horner's method * - base-to-decimal conversion * * NOTE: These functions assume that correct data is input, and the class * has (or will have) a different function for input validation. Your valuable * feedback is always welcome :) */ #include #include #include #include #include using symbol_table = std::unordered_map; // map of chars to their base values inline auto getDigit(char ch) { static symbol_table symbols{ {'0',0}, {'1',1}, {'2',2}, {'3',3}, {'4',4}, {'5',5}, {'6',6}, {'7',7}, {'8',8}, {'9',9}, {'A',10},{'B',11}, {'C',12}, {'D',13},{'E',14}, {'F',15}}; return symbols[ch]; } /* Function Prototypes */ int getIntegerPart(const size_t, const std::string&); double getFractionalPart(const size_t, const std::string&); std::string baseToDecimal(const size_t, std::string const&); /* Test functions */ int main() { const size_t radix = 2; std::string number("10111.10101"); std::cout << number << " (base " << radix << ") = " << baseToDecimal(radix,number) << "(base 10)\n"; return 0; } double getFractionalPart(const size_t radix, const std::string &s) { double product = 0.0; // if number does not have a radix point then return product, i.e. 0 if(s.empty()) return product; const double oneOverBase = 1.0/radix; int digit{0}; // prefer using STL algorithms for_each(s.crbegin(), s.crend(), [&](const char ch){ product += getDigit(std::toupper(ch)); product *= oneOverBase; }); return product; } int getIntegerPart(const size_t radix, const std::string& s) { // if integer part is 0 return 0 immediately if(s.empty()) return 0; int sum{0}; for_each(s.cbegin(), s.cend(), [&](char const ch) { sum *= radix; sum += getDigit(std::toupper(ch)); }); return sum; } std::string baseToDecimal(const size_t radix, std::string const& s) { if(radix != 10) { std::string intpart{""}, fracpart{""}; if(auto pos = s.find('.'); pos != std::string::npos) { // split the input string // in int and decimal part // upfront and thus avoid // checking for position of // decimal point intpart = s.substr(0, pos); fracpart = s.substr(pos+1); } else { intpart = s; } return std::to_string( getIntegerPart( radix, intpart )+ getFractionalPart(radix,fracpart)); } return s; }

base_to_decimal(refactored for GTT.cpp