Compile-time rational arithmetic
From cppreference.com
                    
                                        
                    
                    
                                                            
                    The class template std::ratio and associated templates provide compile-time rational arithmetic support. Each instantiation of this template exactly represents any finite rational number.
[edit] Compile-time fractions
| Defined in header  <ratio> | |
| represents exact rational fraction (class template) | |
Several convenience typedefs that correspond to the SI ratios are provided by the standard library:
| Defined in header  <ratio> | |
| Type | Definition | 
| yocto | std::ratio<1, 1000000000000000000000000>, if std::intmax_t can represent the denominator | 
| zepto | std::ratio<1, 1000000000000000000000>, if std::intmax_t can represent the denominator | 
| atto | std::ratio<1, 1000000000000000000> | 
| femto | std::ratio<1, 1000000000000000> | 
| pico | std::ratio<1, 1000000000000> | 
| nano | std::ratio<1, 1000000000> | 
| micro | std::ratio<1, 1000000> | 
| milli | std::ratio<1, 1000> | 
| centi | std::ratio<1, 100> | 
| deci | std::ratio<1, 10> | 
| deca | std::ratio<10, 1> | 
| hecto | std::ratio<100, 1> | 
| kilo | std::ratio<1000, 1> | 
| mega | std::ratio<1000000, 1> | 
| giga | std::ratio<1000000000, 1> | 
| tera | std::ratio<1000000000000, 1> | 
| peta | std::ratio<1000000000000000, 1> | 
| exa | std::ratio<1000000000000000000, 1> | 
| zetta | std::ratio<1000000000000000000000, 1>, if std::intmax_t can represent the numerator | 
| yotta | std::ratio<1000000000000000000000000, 1>, if std::intmax_t can represent the numerator | 
[edit] Compile-time rational arithmetic
Several alias templates, that perform arithmetic operations on ratio objects at compile-time are provided.
| Defined in header  <ratio> | |
| (C++11) | adds two ratioobjects at compile-time(alias template) | 
| (C++11) | subtracts two ratioobjects at compile-time(alias template) | 
| (C++11) | multiplies two ratioobjects at compile-time(alias template) | 
| (C++11) | divides two ratioobjects at compile-time(alias template) | 
[edit] Compile-time rational comparison
Several class templates, that perform comparison operations on ratio objects at compile-time are provided.
| Defined in header  <ratio> | |
| (C++11) | compares two ratioobjects for equality at compile-time(class template) | 
| (C++11) | compares two ratioobjects for inequality at compile-time(class template) | 
| (C++11) | compares two ratioobjects for less than at compile-time(class template) | 
| (C++11) | compares two ratioobjects for less than or equal to at compile-time(class template) | 
| (C++11) | compares two ratioobjects for greater than at compile-time(class template) | 
| (C++11) | compares two ratioobjects for greater than or equal to at compile-time(class template) |