C Language foundation Day4- Array

One 、 To define an array

  Store several variables of the same data type in a continuous memory , All members in the same array have the same data type , At the same time, the addresses of all members in memory are consecutive .

Two 、 Declare an array

• The type of each element in the array is determined by the type in front of the array name
• The number of elements in the array is determined by [] The value inside determines
• When defining an array ,[] The value inside cannot be a variable , It can only be constant
• Using arrays ,[] The value inside can be a constant or a variable
• Numeric arrays cannot be manipulated as a whole
• Every element of the array is a variable

int num[10];

int num[10] = {
    1,2,3,4,5,6,7,8,9,10};

//  If the array initializes only some elements , Other elements are initialized to 0
int num[10] = {
    1,2};
int num[10] = {
    0};//  Initialize all elements of the array to 0
int num[10] = {
    [5] = 5};//  Mark the subscript as 5 The element of is assigned the value of 5

int num[] = {
    1,2,3};// [] No value in   The number of elements in this array is determined by {} The number of elements inside determines 

3、 ... and 、 Length of array

int num[10] = {
    0};
int n = sizeof(num) / sizeof(num[0]);//  The length of the array 

Four 、 How to store arrays in memory

  Start a program , The system will allocate a piece of memory space to the program ; The smallest unit of memory is a byte , Every byte in memory has a number , This number is the address in memory .

Address of data in memory , Is its starting address in memory .

such as ,int b, Occupy four bytes of memory , Then the addresses occupied by these four bytes are ：0x1001、0x1002、0x1003、0x1004, that b The memory address of is the starting address :0x1001.

• explain ：
  • a[0] The first 0 Elements
  • &a[0] The first 0 Addresses of elements == 01
  • Array name a Representative array , Also stands for the 0 Addresses of elements a == &a[0] == 01, So the array name is a constant , It's an address .
  • &a Get the address of the entire array == 01 In numerical terms &a[0],a,&a, equal , But the meaning is different
  • &a[0] + 1 Add one to the address of the element Across an element == 05
  • a+1 Add one to the address of the element Across an element == 05
  • &a + 1 Add one to the address of the entire array , Across the entire array == 21

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	int a[5];
	printf("%u\n",&a[0]);
	printf("%u\n",a);//  Array name   It's the address of the first element 
	printf("%u\n",&a);//  Take out   Address of array 

	printf("%u\n",&a[0] + 1);// The first element of the array   Add one   Across an element  + 4
	printf("%u\n",a + 1);//  Add one to the address of the element   Across an element 
	printf("%u\n",&a + 1);//  Add one to the address of the entire array   Across the entire array 

	return 0;
}

5、 ... and 、 Bubble sort

Bubble sort ： Compare two adjacent elements , The front one is bigger than the back one , Exchange two elements , If the array has n Elements , Then you need to exchange in total n - 1 round , Every time i Round exchange n - i Time .

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	int a[5] = {
    2,5,6,3,-1};
	/*printf("%u\n",&a[0]); printf("%u\n",a);//  Array name   It's the address of the first element  printf("%u\n",&a);//  Take out   Address of array  printf("%u\n",&a[0] + 1);// The first element of the array   Add one   Across an element  + 4 printf("%u\n",a + 1);//  Add one to the address of the element   Across an element  printf("%u\n",&a + 1);//  Add one to the address of the entire array   Across the entire array */

	int n = sizeof(a) / sizeof(a[0]);//  Calculate how many elements the array has   Divide the length of all bytes of the array by the length of a single element 

	for (int i = 0; i < n - 1; i++)
	{
    
		//  The outer loop   It mainly controls the number of cycles 
		//  Inner circulation mainly controls the comparison times of each cycle 
		for (int j = 0; j < n - i - 1; j++)
		{
    
			if (a[j] > a[j+1])
			{
    
				//  Exchange elements 
				int t = a[j];
				a[j] = a[j+1];
				a[j+1] = t;
			}
		}
	}

	for (int i = 0; i < n; i++)
	{
    
		printf("%d ",a[i]);
	}

	return 0;
}

6、 ... and 、 Two dimensional array

• A two-dimensional array is conceptually two-dimensional ： Its subscript changes in two directions , Access to it usually requires two subscripts
• There is no two-dimensional array in memory , The actual hardware memory of two-dimensional array is continuously addressed , That is, there are only one-dimensional arrays in memory , That is, put one line in sequence after the second line , It's the same way as a one-dimensional array .
• int a[2][4] Defines a two-dimensional array , A two-dimensional array has two one-dimensional , Each one-dimensional array has four elements , Then the two-dimensional array a[0] On behalf of the 0 That's ok

6.1 Initialization of an array

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	int a[3][4] = {
     {
    1,2,3,4},{
    5,6,7,8},{
    9,10,11,12} };//  Initialization of 2D array 

	//  If you initialize some elements of a two-dimensional array , The other elements are 0
	int b[3][4] = {
     1,2,3 };

	int c[3][4] = {
    1,2,3,4,5,6,7,8,9,10,11,12};//  Two dimensional arrays are essentially one-dimensional arrays   Subscripts can be calculated automatically 

	int d[][3] = {
     1,2,3,4,5 };//  When defining a two-dimensional array   The subscript of the column cannot be omitted   The subscript of the line can be omitted   The subscript of a row can be calculated automatically 

	for (int i = 0; i < 2; i++)
	{
    
		for (int j = 0; j < 3; j++)
		{
    
			printf("%d ",d[i][j]);
		}
	}

	return 0;
}

6.2 Calculate the number of rows and columns of the array

• Calculate the total number of array elements ：sizeof(a) / sizeof(a[0][0]);
• Calculate the number of rows of the array ：sizeof(a) / sizeof(a[0]); a[0] Represents the size of a row of elements
• Calculate the number of columns in the array ：sizeof(a[0]) / sizeof(a[0][0]); Divide the number of bytes of a line of elements by the number of bytes of an element

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	int a[3][4] = {
     {
    1,2,3,4},{
    5,6,7,8},{
    9,10,11,12} };//  Initialization of 2D array 

	int n = sizeof(a) / sizeof(a[0][0]);//  Calculate the total number of elements 
	int row = sizeof(a) / sizeof(a[0]);//  Calculate the number of rows of the array   Divide the size of a two-dimensional array by the size of a row 
	int column = sizeof(a[0]) / sizeof(a[0][0]);//  Calculate the number of columns in the array   Divide the size of a row by the size of an element 

	printf("%d %d %d\n",n,row,column);
	
	return 0;
}

6.3 Array name

int a[2][3];

* a[0][0]    The first 0 Xing di 0 Elements 
* &a[0][0]   The first 0 Xing di 0 Addresses of elements 
* a[0]   On behalf of the 0 Array name of row one-dimensional array , Also stands for the 0 Address of row one-dimensional array a[0] = &a[0][0]
* &a[0]  The first 0 The address of the line  = 01
* a  Array name of two-dimensional array   Represents a two-dimensional array , Also represents the first line address &a[0]
* &a  Address of two-dimensional array 

* &a[0][0] + 1   Element address plus 1, Across an element 
* a[0] + 1       Add one to the element address , Across an element 
* &a[0] + 1      Line address plus one , Cross a line 
* a + 1          Line address plus one , Cross a line 
* &a + 1         Two dimensional array address plus one , Across the entire array 

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	int a[3][4] = {
     {
    1,2,3,4},{
    5,6,7,8},{
    9,10,11,12} };//  Initialization of 2D array 

	int n = sizeof(a) / sizeof(a[0][0]);//  Calculate the total number of elements 
	int row = sizeof(a) / sizeof(a[0]);//  Calculate the number of rows of the array   Divide the size of a two-dimensional array by the size of a row 
	int column = sizeof(a[0]) / sizeof(a[0][0]);//  Calculate the number of columns in the array   Divide the size of a row by the size of an element 

	printf("%d %d %d\n",n,row,column);

	printf("%u\n",&a[0][0]);
	printf("%u\n",a[0]);
	printf("%u\n",&a[0]);
	printf("%u\n",a);
	printf("%u\n",&a);

	printf("%u\n",&a[0][0] + 1);//  Just add an element address 
	printf("%u\n",a[0] + 1);//  Just add the address of one element 
	printf("%u\n",&a[0] + 1);//  Add the address of a line of elements 
	printf("%u\n",a + 1);//  Add the address of a line of elements 
	printf("%u\n",&a + 1);//  Add the element address of the entire array 

	
	return 0;
}

7、 ... and 、 Multidimensional arrays

 int num[2][3][4]; Defines a three-dimensional array , There are two two-dimensional arrays , Each two-dimensional array has three one-dimensional arrays , Each one-dimensional array has four elements .

8、 ... and 、 A character array

  A string is an array of characters with \0 An array of characters , Because there is \0 A character array of characters , Easy to operate , Numbers 0（ character ’\0’ Of ACSII code ） At the end of the char An array is a string , But if chaR The array is not numbered 0 ending , Then it's not a string , Just an ordinary character array , So string is a special kind of char Array .

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	char a[5] = {
    'a','b','c','d','\0'};//  The character array contains \0 Character   It's just a string 
	char b[5] = "abcd";//  Defines a character array   Deposit is abcd\0
	char c[] = "world";//  The length of the array is 6  character string 
	char d[100] = "abc";//  Defines a character array   Yes 100 Elements   The other elements are \0
	char e[100] = {
    0};//  Clear a character array 0 0 Is the character '\0'  Of acsii code 

	for (int i = 0; i < sizeof(a) / sizeof(a[0]); i++)
	{
    
		printf("%d ",a[i]);//  Single print character   Print in decimal form 
	}
	printf("\n");
	//  Character arrays can also be printed as strings   Just until the first address of the array 
	printf("%s\n",a);
	printf("%s\n",b);
	printf("%s\n",c);
	printf("%s\n",d);
	printf("%s\n",e);//  All spaces 
	
	return 0;
}

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	char a[128] = "abcd\0def\0";

	printf("%d\n",sizeof(a));// 128
	printf("%s\n",a);//  Print abcd
		

	return 0;
}

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	char a[] = {
    'a','b','c'};//  An ordinary character array 
	printf("%d\n",sizeof(a));//  Output 3
	printf("%s\n",a);//  No characters 0  ending   Output abc Scald   The statement 
	return 0;
}

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	char a[] = {
    'a','b',0,'c'};//  There is 0  Express '\0'
	char b[] = {
    'a','b','0','c',0};//  In the middle of the 0 Characters will be printed   because acsii yes 48
	char c[] = {
    'a','b','c','\0','v'};//  Print abc

	printf("%s\n",a);//  Print ab
	printf("%s\n",b);//  Print ab0c
	printf("%s\n",c);//  Print abc

	return 0;
}

Nine 、scanf Input string

At the end of a carriage return , It ends when you encounter a space , meanwhile , If the space for storing read characters is insufficient , Continue to want to store characters later , No, ’\0’ character , When printing, all characters will be printed directly , Even if it exceeds the length of the character array , This causes memory pollution

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	char num[128] = "";//  Character array clear 0
	scanf("%s",num);//  Get a string from the keyboard   At the end of a carriage return   There is no need to take the address character 
	printf("%s\n",num);// %s  What you want is to print the address of the first element of the character array 

	return 0;
}

Ten 、gets function

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	// gets Function encountered \n end   But it won't end when encountering spaces   Read spaces   But it will also cause memory pollution 
	char num[128] = "";//  Character array clear 0
	gets(num);//  The parameter is the address where the read string is stored 
	printf("num = %s\n",num);

	return 0;
}

11、 ... and 、fgets() function

  Library function ： Read a string from the keyboard ;char num[128]; fgets(num,sizeof(num),stdin);// fgets from stdin（ The standard input - keyboard ） Read string to num Array , It can be read at most sizeof(num) - 1 Characters , Because you need to add ’\0’;

• How to reset the last character to ’\0’

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)

int main()
{
    
	char buf[128] = "helloA";

	//  Set the last character of the string to '\0'
	//  First you need to find the subscript of the last character 
	//  Find the number of valid characters of the character array 

	int i = 0;
	while (buf[i] != '\0')
	{
    
		i++;
	}
	//  Last i  Dropped the subscript 6 The location of 
	printf("%d\n",i);

	buf[i - 1] = '\0';//  Set the last character to '\0'
	printf("%s\n",buf);//  Print hello

	return 0;
}

Use strlen() Function to calculate the number of valid characters of a character array , Then set the last character to ’\0’

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)
#include<stdlib.h>
#include<string.h>

int main()
{
    
	char buf[128] = "helloA";

	//  Set the last character of the string to '\0'
	//  First you need to find the subscript of the last character 
	//  Find the number of valid characters of the character array 

	int i = strlen(buf);// strlen()  Calculate the number of valid characters in the character array 

	buf[i - 1] = '\0';//  Set the last character to '\0'


	printf("%s\n",buf);//  Print hello

	return 0;
}

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)
#include<stdlib.h>
#include<string.h>

int main()
{
    
	//fgets Will read the Enter key 
	char buf[1024] = "";
	fgets(buf,sizeof(buf),stdin);//  Read newline 
	buf[strlen(buf) - 1] = '\0';//  Set the newline character directly to '\0'
	printf("%s\n",buf);//  Print hello

	return 0;
}

Twelve 、 Output of character array

• puts、fputs function

#include<stdio.h>
#define _CRT_SECURE_NO_WARNINGS
#pragma warning(disable:4996)
#include<stdlib.h>
#include<string.h>

int main()
{
    
	char buf[1024] = "helloworld";
	puts(buf);//  Automatically output a line feed 
	fputs(buf,stdout);//  The first parameter , The address of the first element of the array  stdout standard output （ The screen ）


	return 0;
}