How to convert a double to a float type

If you don't think about the problem of loss:

Floating-point variables can be promoted to a larger cardinality type (from float to double). When you perform arithmetic on floating-point variables, a boost usually occurs. This arithmetic is always performed with as high precision as the variable with the highest precision.

For example, consider the following types of declarations:

float f_short;double f_long;long double f_longer;f_short = f_short * f_long;

In the previous example, the variable f short is promoted to type double and multiplied by f long; The result is then rounded to type float and assigned to f short.

double to float, if the value is not out of bounds, the following is an example:

void main()

double a=;

float b;

b = (float) a;

printf("%f",b);

If the numeric range is out of bounds, it should not be converted.

You have to understand it in terms of the storage space applied for by double and float.

In C, double applies twice as much memory space as float, and if you cast it will lose data, only take the following digits.

If you have to convert, the caster is (float), e.g. b = (float) a;

float f = ;

double d =

Cutover is designed to be a precision issue, so you need to use strings to ensure that you don't lose data.

is converted to float type, not double.

float a = without f after ; In this case, floats are automatically considered to be of type double, but float by definition, so there will be type conversions.

The double type occupies 8 bytes in memory, and the int type occupies 4 bytes in memory. The value of double is greater than int. It can be understood that the double is an 8-liter kettle, and the int type is a 4-liter kettle, and the water from the large kettle cannot be poured directly into the small kettle.

If you want the value to be successfully assigned, you need to cast the int type to the double type.

Forced type conversion: Convert a data type with a large value range to a data type with a small value range, which is performed automatically, while the coercion needs to be performed manually.

Conversion Format: Data Type Variable Name = Data Type) The data value to be transformed.

Assign value to int type, modify to int i = int); The double type is converted to the int type, and the decimal point is directly removed.

Strong note: Converting floating-point numbers to integers and removing the decimal point directly will result in a loss of precision.

int is forcibly converted to short and chops off two bytes, which may cause data loss.

1. The range of indicators is differentThe index range of the float is -127 128.

The index range for double and double is -1023 10242. The expression index is differentThe expression for float is 1 bit (sign bit) + 8 bits (exponential bit) + 23 bits (mantissa bit).

The expression of double is 1 bit (sign bit) + 11 bits (exponential bit) + 52 bits (mantissa bit).

3. The number of significant digits is differentFloats can only provide seven significant digits.

Double can provide 16 significant digits.

4. The memory space occupied is differentfloat occupies 4 bytes (32 bits) of memory space, and the value range is .

double occupies 8 bytes (64-bit) of memory space, and the value range is .

%f and %lf are the float type and double type, respectively, and are used to format the input and output symbols. So after changing to float, you have to change lf to f

float: single-precision floating-point data, double: double-precision floating-point data.

The precision of float and double is determined by the number of digits of the mantissa number. Floating-point numbers are stored in memory according to scientific notation, and their integer part is always an implicit "1" because it is invariant', so it cannot affect the accuracy.

float: 2 23 = 8388608, a total of seven digits, which means that there can be up to 7 significant digits, but the absolute guarantee is 6 digits, that is, the accuracy of the float is 6 7 significant digits;

double: 2 52 = 4503599627370496, a total of 16 bits, in the same way, the precision of double is 15 16 bits.

Because float can have up to 7 significant digits, float x = 51539607552, after subtracting 1000, the significant digit remains the same, and double x can be calculated as 11 digits.

The usage is as follows:Double is a commonly used doubleprecision floating-point number format in the C language. Its storage space occupies 8bit, can represent the number of decimal places more accurate than real numbers or singleprecision (singleprecision), such as the decimal decimal precision reaches 15 17 bits, the hexadecimal decimal precision reaches 30 34 bits, its calculation accuracy is close to ten times that of the machine, and there is no need to overflow when calculating the power of 2, which is suitable for storing actual data that requires higher accuracy, such as geographic data, date and time, and other conversion of actual data with higher requirements.

Float is a singleprecision floating-point number format in the C language, which occupies 4 bits of storage space and can represent decimal decimal precision up to 7 8 digits and hexadecimal decimal precision up to 15 bits. It only takes up a limited amount of memory space, which is half less than the double type, but using the float type to calculate two real number operations may give incorrect results, which is suitable for calculations that require lower precision when storing actual data, such as plots and animations.

Therefore, float and double complete two different functions, they meet the requirements of different data representation accuracy, when storing and calculating data, choose to use float or double according to the needs, can more effectively realize data storage, computing and processing and other operations, will help accelerate the efficiency of computer system operation, and contribute to the development of computer science and computer technology.