2. Floating point number, the difference between float and double in C language and how to choose them

1. First we need to know ,float,double stay C The language means The set of real Numbers , And decimals in C In language The default is double type .
2. float It belongs to single precision floating-point data ,double It belongs to double precision floating-point data . The meaning of this sentence is double The accuracy of higher than float.float Occupy 4 Bytes of memory , and double Occupy 8 Bytes .
3. float Only available 6 Significant digits , Generally speaking, absolutely 6 position , Probably 7 It should be 6~7 position ,double Can provide 16 Significant digits .
4. Generally speaking ,CPU Processing single precision floating-point numbers is faster than processing double precision floating-point numbers , If you don't declare , The default decimal is double type , So if you want to use float Words , It has to be forced to turn ,eg:float a = 1.24546f;

       float a = 1.24324556;
       double b = 1.24324556;
       float c = 1.24324556;
       double d = 1.24324556;
       printf("a=%f\n", a);
       printf("b=%f\n", b);
       printf("c=%.8f\n", c);
       printf("d=%.8f\n", d);

   

   1. We go through a and b The output of can be seen ,%f perhaps %lf Indicates that the default output is six decimal places , Less than six to 0 A filling , More than six digits are rounded off .

   2. adopt c and d The output of can be seen %.8f It means to output eight decimal places , and float type Of C Because it can only be kept after the decimal point 6~7 position , So it is rounded , and double Type of d It can output accurately .

How to select and use float still double Well ？

         For programmers ,double and float Is the difference between the double High precision , Significant figures 16 position ,float precision 7 position . but double Memory consumption is float Twice as many ,double The speed of computing is faster than float Much slower ,C The name of mathematical function in language double and float Different , Don't write wrong , Don't use double precision when you can use single precision （ To save memory , Speed up the calculation ）.