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  1. #include <iostream>
  2. #include <cstring>
  3. #include <cmath>
  4. #include <algorithm>
  5. using namespace std;
  6.  
  7. int num(char c)  // цифра в некоторой системе счисления
  8. {
  9.     const char digs[] = "0123456789abcdefghijklmnopqrstuvwxyz";
  10.     return int(strchr(digs, tolower(c)) - digs);
  11. }
  12.  
  13. // Строка с числом в системе счисления base в double
  14. // Защиты от дурака нет!
  15. double toNum(const char* s, int base)
  16. {
  17.     if (base < 2 || base > 36) throw range_error("Wrong base");
  18.     const char* c;
  19.     double r = 0;
  20.     for (c = s; *c && *c != '.'; ++c)
  21.         r = r * base + num(*c);
  22.     if (*c == '.')
  23.     {
  24.         for (double bs = base; *++c && bs > 0; bs *= base)
  25.             r += num(*c) / bs;
  26.     }
  27.     return r;
  28. }
  29.  
  30. // Число double в строку в системе счисления base, с prec знаков после точки
  31. // Защиты от дурака нет!
  32. string fromNum(double x, int base, int prec = 6)
  33. {
  34.     const char digs[] = "0123456789abcdefghijklmnopqrstuvwxyz";
  35.     if (base < 2 || base > 36) throw range_error("Wrong base");
  36.     int d = floor(x);
  37.     string r;
  38.     if (d == 0) r = "0";
  39.     else
  40.     {
  41.         while (d)
  42.         {
  43.             r += digs[d % base];
  44.             d /= base;
  45.         }
  46.         reverse(r.begin(), r.end());
  47.     }
  48.     x = x - floor(x);
  49.     if (x && prec > 0)
  50.     {
  51.         r += '.';
  52.         for (int i = 0; i < prec; ++i)
  53.         {
  54.             x *= base;
  55.             r += digs[int(x)];
  56.             x = x - floor(x);
  57.         }
  58.     }
  59.     return r;
  60. }
  61.  
  62.  
  63. // Простенький тест...   
  64. int main(int argc, char* argv[])
  65. {
  66.     string seven = "1234.56";
  67.     cout << "orig: " << seven << endl;
  68.     double x = toNum(seven.c_str(), 7);
  69.     cout << "x = " << x << endl;
  70.     string elev = fromNum(x, 11, 20);
  71.     cout << "11: " << elev << endl;
  72.  
  73.  
  74.     x = toNum(elev.c_str(), 11);
  75.     cout << "x = " << x << endl;
  76.     elev = fromNum(x, 4, 20);
  77.     cout << "4: " << elev << endl;
  78.  
  79.  
  80.     x = toNum(elev.c_str(), 4);
  81.     cout << "x = " << x << endl;
  82.     elev = fromNum(x, 7, 20);
  83.     cout << "7: " << elev << endl;
  84. }
  85.  
Success #stdin #stdout 0s 4980KB
comments (?)
stdin 
Standard input is empty
stdout 
orig: 1234.56
x = 466.837
11: 394.92276a6074542268188a
x = 466.837
4: 13102.31120310033223012201
x = 466.837
7: 1234.55666666666666260026
https://ideone.com/7yit22
language:
C++14 (gcc 8.3)
created:
4 years ago
visibility:
public

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