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  1. #include <iostream>
  2. #include <iomanip>
  3. #include <limits>
  4. #include <math.h>
  5. #include <sstream>
  6. using namespace std;
  7.  
  8. void test(double value)
  9. {
  10.     int digits_before = 1 + (int)floor(log10(fabs(value)));
  11.     int digits_after = std::numeric_limits<double>::digits10 - digits_before;
  12.     double whole = floor(pow(10, digits_after) * fabs(value) + 0.5);
  13.     while (digits_after > 0 && (whole/10.0 - floor(whole/10.0)) < 0.05)
  14.     {
  15.         --digits_after;
  16.         whole = floor(whole / 10.0 + 0.5);
  17.     }
  18.     if (digits_after < 0) digits_after = 0;
  19.     std::stringstream ss;
  20.     ss << std::fixed << std::setprecision(digits_after) << value;
  21.     cout << ss.str() << endl;
  22. }
  23.  
  24. int main() {
  25. 	test(3.14);
  26. 	test(3.14159);
  27. 	test(1000);
  28. 	test(1000.00000000001);
  29. 	test(0.00001);
  30. 	test(0.000000000000000000023);
  31.     return 0;
  32. }
Success #stdin #stdout 0s 3476KB
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stdin
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Standard input is empty
stdout
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3.14
3.14159
1000
1000.00000000001
0.00001
0.000000000000000000023
https://ideone.com/HAk55Y
language:
C++14 (gcc 8.3)
created:
11 years ago
visibility:
public

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