C language: data types

variable

1. C language identifiers include variables, function names, macro definition, the structure member name.
2. C language identifier must be specified in a letter or an underscore _at the beginning, it can be followed by a number of letters, numbers, underscores, there can be other characters.
3. Keywords can not be defined as an identifier.

C language keywords

auto 	break	 case	 char	 const 	continue 	default	 do		double
else 	enum 	 extern	 float	 for 	goto	    if 	     int	long
register return  short   signed  sizeof static      struct   switch typedef
union   unsigned void    volatile while

Type Size

32-bit operating system

#include<iostream>

using std::cout;
using std::endl;

int main()
{
	cout <<"char->"<< sizeof(char) << endl;
	cout <<"short->"<< sizeof(short) << endl;
	cout << "int->"<<sizeof(int) << endl;
	cout << "long->"<<sizeof(long) << endl;
	cout <<"long long ->"<< sizeof(long long) << endl;
	cout << "float->"<<sizeof(float) << endl;
	cout << "double->"<<sizeof(double) << endl;
	cout << "long float->"<<sizeof(long float) << endl;
	cout << "long double->"<<sizeof(long double) << endl;
	system("pause");
	return 0;
}

char->1
short->2
int->4
long->4
long long ->8
float->4
double->8
long float->8
long double->8
请按任意键继续. . .

64-bit operating system

#include<iostream>

using std::cout;
using std::endl;

int main()
{

    cout <<"char->"<< sizeof(char) << endl;
    cout <<"short->"<< sizeof(short) << endl;
    cout << "int->"<<sizeof(int) << endl;
    cout << "long->"<<sizeof(long) << endl;
    cout <<"long long ->"<< sizeof(long long) << endl;
    cout << "float->"<<sizeof(float) << endl;
    cout << "double->"<<sizeof(double) << endl;
    cout << "long double->"<<sizeof(long double) << endl;
    return 0;
}

char->1
short->2
int->4
long->8
long long ->8
float->4
double->8
long double->16

difference

32-bit longlength of the system is 4,64 bit longlength is 8.
32-bit long floatlength is 8,64-bit operating system long floatis not legal data type.

Initialize an array of three characters following differences:

char arr1[]="abc"           //'a''b' 'c' '\0'
char arr2[]={'a','b','c'};  //'a''b' 'c' 
char *p="abcdef";           //p的内存中只存了字符a的地址

• 1, the memory array is stored in a row.
• 2, a memory cell in the memory (one byte) corresponding to a memory address.
• 3, the 32-bit pointer size is 4 bytes platform, the platform 64 is 8 bytes.
• 4, can be understood as a pointer variable, is specifically designed to store the address of a variable.

% Lf% l and distinction of

C ++ really is very subtle language,% f and% lf for printf () and scanf () effect is different

#include<stdio.h>
int main()
{
    float n;
    scanf("%lf",&n);
    printf("%f",n);
    return 0;
}

80
0.000000

Solution: 1) the "% lf" was changed to "% f"; 2) will be replaced by double float

In fact, the printf (), whether or% f% lf, the effect is the same. Because, face float, printf () will float type automatically promoted to double, so it will not have any problems. And, strictly speaking, printf () and no definition of% lf, although many compilers will accept, so it is best to use% f.
For scanf (), by accepting a pointer, and no type of argument upgrade, so it should be used for double% lf, float is% f.