精度:
float: 3e38
double: 1.7e308
显示
cout<<fixed<<a<<endl; 一般显示
cout<<scientific<<b<<endl; 科学计数法
cout<<setprecision(c)<<endl; 设置显示精度
1 #include <iomanip> 2 #include <iostream> 3 4 using namespace std; 5 6 int main() { 7 // Creating a decimal double type variable 8 double a = 3.912348239293; 9 10 // Creating an exponential double type variable 11 double ex1 = 325e+2; 12 13 // Creating a float type variable 14 float b = 3.912348239293f; 15 16 // Creating an exponential float type variable 17 float ex2 = 325e+2f; 18 19 // Displaying output with fixed 20 cout << "Displaying Output With fixed:" << endl; 21 cout << "Double Type Number 1 = " << fixed << a << endl; 22 cout << "Double Type Number 2 = " << fixed << ex1 << endl; 23 cout << "Float Type Number 1 = " << fixed << b << endl; 24 cout << "Float Type Number 2 = " << fixed << ex2 << endl; 25 26 // Displaying output with scientific 27 cout << "\nDisplaying Output With scientific:" << endl; 28 cout << "Double Type Number 1 = " << scientific << a << endl; 29 cout << "Double Type Number 2 = " << scientific << ex1 << endl; 30 cout << "Float Type Number 1 = " << scientific << b << endl; 31 cout << "Float Type Number 2 = " << scientific << ex2 << endl; 32 return 0; 33 }
比较大小
predicate 翻译过来叫 谓词
A predicate is the part of a sentence that contains the verb and tells you something about the subject. 也就是显示主语的状态. 而在计算机领域, 可能这个状态就更多地true和false来表示.
1 class pig 2 { 3 bool is_eating(){}; 4 }
在上面, dog.is_barking()就是谓词, 这可能代表着我们 是否应该喂猪
double 类型不能直接用> < ==来比较大小, 需要一个类似predicate的东西, 也就是要设置一个容差
1 #include <math.h> 2 const double EPS = 1e-8; 3 4 if(fabs(a-b) < EPS) //绝对值小于容差, 就认为两个double是相等的了 5 6 if(a > b+EPS) // 判断a是否大于b，因为大的肯定大，所以即使你小的加上，还是会更大