Chapter C data types

Octal integer number of 0 at the beginning, followed by a sequence of numbers consisting of 0 to 7.

The letters hexadecimal integer x (or X) at the beginning, followed by the numbers 0 to 9, 0, a ~ f (or A ~ F) in a sequence of numbers.

Integer constants:

Is defined as the default type int signed integer, so the type without using signed int
Unsigned integer constant: U
Long integer constant: L
Unsigned long integer constant: LU

Decimal form

Exponential form: 3.45e-6 = 0.00000345

Real constants:

Single-precision: F
Double precision (real constant default)
Long double precision: L

Variables must be defined before use, you need to type the variable name and variable declarations.

// L2-1a-1

main () // in main () as the starting point C designates the beginning of a program executed 
// a C program must have one and only one with a main () function as a name, called main function { 
    int    A; 
    a float B;             
    char  C;  A. 1 = ;  B = 2.5 ; C = 'A' ;}

Variable names (identifiers) are case sensitive
All variables must be defined before the first executable statement
Space program is to enhance the readability
Definitions of the variables can be simultaneously initialized variables, such as int a = 1;

// L2-1a-2

main () 
{ 
    int a =. 1; / * define integer variables and initializes a * / 
    a float b = 2.5; / * define a real variable b and initializes * /         
    char C = 'A'; / * define c string variables and initializes * /         
}

The same can also define a plurality of variables, such as int a, b, c;

Comments can not be nested!

// L2-1b

#include <stdio.h> // This is the C preprocessor command 
// This line will appear in each of the data required from the output to the screen or keyboard input program data main () 
{ 
    int = A. 1 ; 
    a float = 2.5 B ;             
    char C = 'a' ;  // \ n-output represents a newline  printf ( "a =% d \ n", a); / * output by the integer format value of a variable * /  the printf ( "B =% f \ n ", b ); / * output by the format real value of the variable b, unless specified otherwise implied decimal output 6 * / the printf ("% C = C \ n-", C); / char * format by the output variable value of c * / the printf ( "End of Program \ n-"); / * output line of the string * / }

// Run Results 
A. 1 = 
B = 2.500000 
C = A 
End of Program

Variable data type or the size of the space occupied:

1B (byte) = 8bit
sizeof () keyword is the C language, not a function name
the sizeof () is a C language specially provided for calculating the number of bytes of the specified data type operator

// L2-2

#include  <stdio.h>
main()
{
    printf("Data type        Number of bytes\n");
    printf("------------  ---------------------\n");
    printf("char                    %d\n", sizeof(char));
    printf("int                     %d\n", sizeof(int));
    printf("short int               %d\n", sizeof(short)); printf("long int %d\n", sizeof(long)); printf("float %d\n", sizeof(float)); printf("double %d\n", sizeof(double)); }

Results // Run
 the Data bytes of type Number The 
----------------------- --------------------- 
char. 1 
int. 4 
Short int 2 
Long . 4 int 
a float. 4 
Double. 8

Assignment expressions are used to assign values to variables

Directional
Left of the equal sign is the variable name can represent a particular unit of storage

Priority of the operations

Comprehensive: left-associative, right associative
C language requires two operands in arithmetic operators are left-associative
Assignment operator is right-associative

Signed integer and unsigned integers

For integer has the same number of words, the absolute value of the largest integer signed integer only half the non-signed integer
Negative numbers in a computer are based on two's-complement form to represent and store
Positive anti-code complement its original code is the same

'S complement subtraction can be converted to the adding process to
S complement can be represented in a uniform manner and +0 -0

Exponent part real number called the exponent, referred to as the fractional part of the mantissa

Exponent bits occupied by the real number determined table range, determines the number of bits occupied by the mantissa accuracy of real numbers
Mantissa sign determines the sign of the real number

The real number of floating-point numbers is not really, but its approximate within a certain range

// L2-3

#include <stdio.h>
main()
{
    float   a;
    double     b;
    a = 123456.789e4;
    b = 123456.789e4;
    printf("%f\n%f\n",a,b); }

// operating results 
1234567936.000000 
1234567890.000000

C Programming Language (two)