l1--Data Structure Introduction and preliminary knowledge

Introduced

How to store large and complex problems in reality in a specific data type and a specific storage structure into the main memory (memory), and on this basis to implement a function (such as finding an element, delete an element, The corresponding operation to sort all the elements is called an algorithm.

Data structure = individual + individual relationship

Algorithm = manipulation of stored data (methods and procedures for solving problems)

Criteria for measuring algorithms

• 1. Time complexity: The approximate number of times the program will be executed, rather than the time of execution;
• 2. Spatial complexity: The maximum memory occupied by the algorithm during execution;
• 3. Degree of difficulty
• 4. Robustness

The status of data structures

The data structure is the core content of the software.

Program = data storage + data manipulation + languages that can be computed for storage (c,c++, etc.)

Preliminary Knowledge-pointers

The importance of pointers: pointers are the souls of C language

Address: Memory unit number, non-negative integer starting from 0, range: 0---ffffffff[0---4g-1]

Pointer: The pointer is the address address is the pointer

Pointer variable: Is the variable that holds the address

#include <stdio.h>intMainvoid){    int* p;//p is a pointer variable, and an int * indicates that the P variable can store only the address of the INT type variable    /*Ps:int * is a whole (define a pointer variable, like int), do not put *p when a whole int p equals to define a p variable int * p equivalent to define a p-pointer variable*/    inti =Ten; intJ; P= &i; J= *p;//equivalent to j = i//the p at this time holds the address I of I, at this time the * play the role of indirect value , *p is equal. printf"i =%d, j =%d, *p =%d\n", I, J, *p); return 0;}/*output Result: I = ten, j = ten, *p = ten*/

Pointers and functions:

#include <stdio.h>voidFint* p)//The same last program: instead of defining a formal parameter named *p, it defines a pointer variable p that is an int * pointer variable type{    *p = -;//the p at this time holds the address I of I, at this time the * play the role of the indirect value (* can only be used in the pointer variable), *P is equal. }intMainvoid){    inti =9; F (&i); printf ("i =%d\n", i); return 0;}/*output Result: i = 100
PS: You can use the above example to make variables between different functions , imagine if there is no pointer variable, you can also make a variable between different functions to use*/

Pointers and Arrays: array names: one-dimensional array namesis a Pointer Constants; it holds a one-dimensional array the address of the first element; Its value cannot be changed; one-dimensional array name point to theis the first element of the array. The relationship between subscript and pointer: A[i] (<==>) * (A + i)

#include <stdio.h>intMainvoid){    inta[5] = {1,2,3,4,5}; printf ("%p\n", A +1); printf ("%p\n", A +2); printf ("%p\n", A +3); printf ("----------------------------\ n"); printf ("%d\n", *a +3);//*a + 3 equivalent to a[0] + 3    return 0;}/*output Result: 0028fef00028fef40028fef8----------------------------4*/

How to modify the contents of an array in the keynote function through the function

1. A pointer variable that holds the first element of the array; 2. An shaping variable that holds the length of an array element.

#include <stdio.h>voidShowarray (int* p,intLen) {    inti; p[0] = -1;//p[0] = = *p;p[i] is the a[i of the main function]     for(i =0; i < Len; ++i) {printf ("%d\n", P[i]); } printf ("-----------------------\ n" );}intMainvoid){    inta[5] = {1,2,3,4,5}; Showarray (A,5);//A is equivalent to &a[0],printf ("%d\n", a[0]); return 0;}/*results: -12345------------------------1*/

Preparatory knowledge-structure

1. Why the structure is present

In order to represent some complex data, the common basic type variable does not meet the requirements.

2. What is a structural body?

A struct is a composite data type that users define themselves according to their actual needs.

3. How to use the structure body

#include <stdio.h>#include<string.h>structstudent{intSID; Charname[ $]; intAge ;};//semicolons cannot saveintMainvoid){    structStudent st = { +,"Zhangsan", -}; printf ("%d%s%d\n", St.sid, St.name, st.age); St.sid= About; strcpy (St.name,"Lisi"); St.age= A; printf ("%d%s%d\n", St.sid, St.name, st.age); structStudent *PST; PST= &St; PST->sid = the;//Pst->sid is equivalent to (*PST). Sid, and (*PST). SID is equivalent to St.sidprintf"%d%s%d\n", St.sid, St.name, st.age); return 0;}/*output: Zhangsan 2099 Lisi 2288 Lisi*/ 

4. Precautions:

• Structural variables cannot be subtraction, but can be assigned to each other;

Common structure variables and pointer variables of structural bodies

#include <stdio.h>#include<string.h>structstudent{intSID; Charname[ $]; intAge ;};//semicolons cannot savevoidFstructStudent *);voidGstructStudent);voidG2 (structStudent *);intMainvoid){    structStudent St; // to allocate good memory F for St  (&St); //g (ST);//direct the global variable (at least 208 bytes) When the argument passes, consumes memory, consumes timeG2 (&AMP;ST);//only 4 bytes//printf ("%d%s%d\n", St.sid, St.name, st.age);    return 0;}voidFstructStudent *PST) {    (*PST). Sid = About; strcpy (PST->name,"Zhangsan"); PST->age = A;}voidGstructStudent St) {printf ("%d%s%d\n", St.sid, St.name, st.age);}voidG2 (structStudent *PST) {printf ("%d%s%d\n", Pst->sid, Pst->name, pst->Age );}/*output Result: Zhangsan*/

Preliminary knowledge-Dynamic memory

#include <stdio.h>#include<malloc.h>intMainvoid){    inta[5] = {1,2,3,4,5};//unable to dynamically control number of leader degrees    inti; intLen; printf ("Please input length:len ="); scanf ("%d", &Len); int* PARR = (int*) malloc (sizeof(int) *Len);  for(i =0; i < Len; ++i) {scanf ("%d/n", &Parr[i]); } printf ("--------------------------\ n");  for(i =0; i < Len; ++i) {printf ("%d\n", * (PARR +i));    } free (PARR); return 0;}/*output: Please input length:len = 323--------------------------234455*/

l1--Data Structure Introduction and preliminary knowledge