c++ (about double and float)

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Some asked me a question about a surpassingly bug in vc++. The original code looked like this:

double index;

      for(index=0.0;index<1.0;index+=0.1)

            cout<<(int)(index*10.0)<<endl;

      //should print 0 1 2 3 4 5 6 7 8 9, but prints 0 1 2 3 4 5 6 7 7 9 9  

I changed double to a float:

      float index;

      for(index=0.0;index<1.0;index+=0.1)

            cout<<(int)(index*10.0)<<endl;

      return 0;

and all went well, I don’t remember the exact reason ( the way float and double resides in memory + conversion issues to an int) but it's obviously not a bug.