C Language---Data structures (built-in, arrays, custom)

An array is a set of ordered data, each of which belongs to the same data type.

Definition of a one-dimensional array:

Type-character array-name [constant-expression]

In a constant expression, you can include constants and symbolic constants, and int a[3+5] is legal. But cannot contain the Int a[n],c language does not allow dynamic arrays.

An int a[2*n] can exist in a child function, but cannot be a static local variable, because the data in the child function is executed, n is confirmed, and can be

The address space in the stack where int n[2*n] is allocated.

When defined, initializes:

1) int a[10] = {0,1,2,..., 9}; Use {}l= brackets

2) int a[10] = {0,1,2,3,4}; Partial assignment, unassigned elements are automatically assigned a value of 0

3) int a[] ={1,2,3,4,5}; You do not need to specify the array length

Reference to one-dimensional data, array name [subscript]

Two-dimensional data definition:

Type-character array-name [constant-expression] [constant-expression]

Reference array names for two-dimensional arrays [subscript] [subscript]

Initialization of two-dimensional arrays

1) int A[3][4] = {{1,2,3,4},{5,6,7,8},{9,10,11,12}}; Each row element is assigned a separate value

2) int a[3][4] = {1,2,3,4,5,6,7,8,9,10,11,12}; All elements are written together to assign values

3) int A[3][4] = {{1},{5},{9}}; For each row element, the value is partially assigned

4) int A[][4] = {1,2,3,4,5,6,7,8,9,10,11,12}; C language can automatically infer the number of travel elements

An array of characters used to hold characters. Each of these elements holds one character. Finally automatically add empty characters ' \ s '

char [10];

Initialization of the character array, char c[10] = {' I ', ' ', ' a ',.... ' Y '}; ' Denotes a space

The string in C is handled in the form of an array of characters, ending with the flag ' \ S ', which represents 0 in ASCII.

You can assign a string to an array of characters.

Char[] = "I am Happy";

If the defined character data length is longer than characters, the system automatically complements '

Char c[10] = {"China"};  printf ("%s", c); Output prints to 5th characters only

The C-language function provides a function for string handling. Must contain #include<string.h>

1) puts (character array);

Char str[] = {"string"};  Puts (str); When the output is converted to \ n,

2) gets (character array);

Char str[10];  Gets (str); Input characters, automatically add ' + '

The puts and get functions can handle only one character array.

3) strcat (string 1, string 2);

Char str1[30] = {""};

Char str2[] = {"China"};

printf ("%s", strcat (STR1,STR2)); STR1 must be large enough to link str2 to str1

4) strcpy (character number 1, string 2);

Char str1[10],str2[] = "China";

strcpy (STR1,STR2); str1 can only be in the form of an array name , the character array 1 must be defined large enough,

When assigning a value, only 6 elements are placed in the first 6 units of the str1 (including ' \ S '), followed by 4 cells, which are still str1 characters .

strncpy (Str1,str2,n); The first n characters of the str2 are copied to the first n characters of the str1 , not including '/'. ‘’

The string cannot be used directly between str1 = STR2

5) strcmp (string 1, string 2);

strcmp (STR1,STR2); Compare str1 and str2 until a different character and ' s ' are present.

STR1 = = str2, return value 0,str1 > str2, return positive integer, str1 < str2, return negative integer

Strings cannot be used directly between STR1 > STR2

6) strlen (character array);

Char str[10] = "China";

printf ("%d", strlen (str)); The output is 5, indicating the actual number of characters, not including '/'

7) strlwr (string); Converts the uppercase of a string to a lowercase letter

8) STRUPR (string);//Convert the lowercase of a string to uppercase

User-defined structure type:

struct struct name {member table column};

struct Student {int num;  Char name[20];} Student1;

Define struct-Body variables:

struct Body name struct variable

struct Student student1; struct type name must be added to the structure

You can also specify struct variables directly without specifying a type name

struct {int num;  Char name[20];} Student1;

1) When defining a struct variable, initialize:

struct Student b = {. Name = "Zhang"}; A reference to a struct member must use the member operator "."

2) refer to members of struct variables by struct variable name. Member Name

Student1.num = 10010;

3) If the member itself is a struct, you can use the "." multiple times. To quote:

Student1.birthday.month

4) struct variables of the same type can be assigned to each other:

Student1 = Student2;

5) You can reference the address of a struct variable, or you can refer to the address of a struct variable member:

&student1.num &student1

To define an array of struct bodies:

struct type array name [array length]

struct person leader[3];

To define a struct-body pointer:

struct Student *pt; If p points to a struct variable stu, struct variable. Member name (stu.num)

(*p). Member name ((*p). Num)

P-> member name (p->num) equivalent

Pointer to an array of struct bodies

struct Student {int num; char name[];};

struct Student stu[3];

struct Student *p;

for (p=stu; p <stu +3; p++);

Using an array or pointer of a struct variable to do function arguments

void input (struct Student stu[]);

The common body type, in the same storage space, stores different data structures and can only select one at a time.

To define a shared body variable:

Union common body Name {member table column} variable table column;

Union Data {int i; char ch; float F;} a,b,c;

Referencing shared body variables: A.I, a.ch, A.F

When using the shared body type data, only one data structure can be stored in the same memory segment for a certain time period

The element that works in the common body is the last assigned value.

a.ch = ' a ';  A.F = 1.5;   a.i=40; The value in a is 40

If the value of a variable can be only a few possible values, it may be defined as an enum (enum) type

declaring enum type: enum [enum name] {enumeration element list}

Enum Weekend {Sun, Mon, Tue, Wed, Thu, Fri, Sat};

Declaring an Enumeration variable: enumeration type name Variable name

Enum Weekend Workday;

The C compiler handles enumeration elements as constants. This is called an enumeration constant, so you cannot assign a value to an enumeration variable.

C language in order, assigning them 0,1,2,,,

printf ("%d", workday); Output the corresponding value

Use a typedef to re-declare the type.

typedef int integer;

typedef struct {int month; int day; int year;}  Date; Declares a new type name date

typedef int NUM[100]; Declares num as an integer array type name num A; A is an integer array name, with 100 elements

typedef char * String; String p, which defines a string as a character type pointer

typedef int (*pointer) (); Declaring pointer as a pointer type to a function

C Language---Data structures (built-in, arrays, custom)