C Language Learning Tutorial Chapter II-Data types, operators, expressions (iii)

Real-Type Quantity

Real constants

The real type is also called a floating-point type. Real constants are also called real numbers or floating-point numbers. In the C language, the real number is only decimal. It has two kinds of forms: decimal form exponential form
1. Decimal number Form
Made up of digital 0~ 9 and decimal points. For example: 0.0,.25,5.789,0.13,5.0,300.,-267.8230 and so on are valid real numbers.
2. Exponential form
Consists of a decimal number, a step code flag "E" or "E", and a step code (only integers, which can be signed). Its general form is a E n (A is decimal, n is a decimal integer) its value is a*10,n such as: 2.1E5 (equal to 2.1*10,5), 3.7E-2 (equal to 3.7*10,) -2*) 0.5E7 (equal to 0.5*10,7), -2.8E-2 (equal to -2.8*1 0,) -2*) The following is not a valid real number 345 (no decimal point) E7 (no digits before the order sign E)-5 (no order sign) 53.-e3 (minus position is not right) 2.7E (no order)
Standard C allows floating-point numbers to use suffixes. A suffix of "f" or "F" means that the number is a float. such as 356f and 356. is equivalent. Example 2.2 illustrates this situation:
void Main ()
{
printf ("%f\n%f\n", 356.,356f);
}
Void indicates that main does not return any value using printf display result end

Real-type variables

The real variables are divided into two types: single and double-precision,
Its type specifier is a float-precision specifier, double double-precision descriptor. In Turbo C, a single precision 4 byte (32-bit) memory space with a value range of 3.4e-38~3.4e+38 and only seven digits valid digits. The double is a 8-byte (64-bit) memory space with a value range of 1.7e-308~1.7e+308, which provides 16-digit valid digits.
The format and writing rules for the description of the real variable are the same as the integer type.
For example: float x,y; (X,y is a single-precision real-type quantity)
Double a,b,c; (A,b,c is a double-precision real-type quantity)
The real constant is not divided into single and double precision, and is treated as double.
void Main ()
{
float A;
Double b;
a=33333.33333;
b=33333.33333333333333;
printf ("%f\n%f\n", a,b);
}
This program illustrates the difference between float and double
A
b
a<---33333.33333
b<---33333.33333333333;;
Show program Results
This program illustrates the difference between float and double
float A;
Double b;
a=33333.33333;
b=33333.33333333333333; As you can see from this example, because a is a single-precision floating-point type, the number of significant digits is only seven digits. And the integer has accounted for five digits, so after the decimal two digits are invalid numbers. B is a double with a valid bit of 16 digits. But Turbo C stipulates a maximum of six digits after a decimal, and the remainder is rounded.
[Practice]//floatint a=32;
float B;
Double D;
b=12345678;
d=b*100;
D=d+a;
d=d+58.123456; ' Vtable
A,2,32
b,4,0.0
d,8,0.0
of Vtable
' Vupdate
1,32
2,0
3,0
2,12345678.00000
3,1234567800
3,1234567832
3,1234567890.123456
of Vupdate
of Practice
[Practice]//1int a=543;
float B;
B=123.123962+a;
b=b-100;
a=b; ' Vtable
a,2,543
b,4,0.0
of Vtable
' Vupdate
1,543
2,0.0
2,123.123962
2,23.123962
1,23
of Vupdate
of Practice