casting - c++ same calculation assigned to int or double gives different results, but only for certain values (is 64.02 a magic number in c++?) -

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• is floating point math broken? 20 answers

i tried assign calculation result variable, , print out. however, depending on type of variable it's assigned to, results different. unexpected results happened values specific calculation.

int main() {      // above 64.02 give unexpected results     // e.g. (100.02 - 100.0) * 100.0      int ((64.02 - 64.0) * 100.0);      double b ((64.02 - 64.0) * 100.0);      cout<<"result: "<<a<<endl; // result: 1, expected result: 2     cout<<"result: "<<b<<endl; // result: 2, expected result: 2      // below 64.02 give right results      int c ((63.02 - 63.0) * 100.0);      double d ((63.02 - 63.0) * 100.0);      cout<<"result: "<<c<<endl; // result: 2, expected result: 2     cout<<"result: "<<d<<endl; // result: 2, expected result: 2      return 0; } 

i know question specific, suspect has implicit type cast. why values >=64.02?

this first ever question on stack overflow, please don't -1 me!!!

64.02 representation floating point 64.01999664306640625. after computation 1.999664306640625, 1 when rounded down int.

63.02 representation 63.020000457763671875, gives 2 after computation, when rounded down int.

some numbers cannot stored float or double.