c++ - Setprecision is Confusing -

i want ask setprecision because i'm bit confused.

here's code:

#include <iostream> #include <iomanip> using namespace std;  int main()  {   double rate = x;   cout << fixed << setprecision(2) << rate; } 

where x = following:

the left side of equation values of x.

1.105 = 1.10 should 1.11

1.115 = 1.11 should 1.12

1.125 = 1.12 should 1.13

1.135 = 1.14 correct

1.145 = 1.15 correct

but if x is:

2.115 = 2.12 correct

2.125 = 2.12 should 2.13

so why in value it's correct it's wrong?

please enlighten me. thanks

there no reason expect of constants in post can represented exactly using floating-point system. consequence, exact halves have may no longer exact halves once store them in double variable (regardless of how iostreams meant round such numbers.)

the following code illustrates point:

#include <iostream> #include <iomanip>  using namespace std;  int main()  {   double rate = 1.115;   cout << fixed << setprecision(20) << rate; } 

output:

1.11499999999999999112 

i recommend taking @ faq.