C language array

Preface

An array is a collection of elements of the same type , In the learning process , One dimensional array and two-dimensional array are the most commonly used .

One dimensional array creation and initialization

One dimensional array creation

The way one-dimensional arrays are created ：

type_t   arr_name  [const_n];
//type_t Is the element type of the exponential group 
//const_n Is a constant expression , Used to specify the size of the array 

The following is an example of array creation ：

// Code 1
int arr1[10];

// Code 2,** This method may cause errors in some compilers , But actually C Language allows you to specify the size of an array with variables **
int count=10;
int arr2[count];

// Code 3
char arr3[10];
float arr4[5]
double arr5[20];

Initialization of one dimensional array

The initialization of an array refers to , Created in array meanwhile Give the array some reasonable initial values .
Examples are as follows ：

int arr1[10] = {
    1,2,3};
int arr2[] = {
    1,2,3,4};
int arr3[5] = {
    1,2,3,4,5};
char arr4[3] = {
    'a',98,'c'};
char arr5[] = {
    'a','b','c'};
char arr6[] = "abcdef" ;

If the number of array elements is not specified when creating an array , Then the number of elements of the array is determined according to the initialization content .

The use of one-dimensional arrays

For the use of arrays, we introduced an operator [] The subscript reference operator is actually the operator of array access .
The code example is as follows ：

#include <stdio.h>
int main()
{
    
  int arr[10]={
    0};// Incomplete initialization of arrays 
  int sz=sizeof(arr)/sizeof(arr[0]);// Count the number of elements in an array 
  int i=0;// Do array subscripts , Array subscript is from 0 Start 
  for(i=0;i<10;i++)
  {
    
      arr[i]=i;// Array assignment 
  }
  for(i=0;i<10;i++)
  {
    
      printf("%d ",arr[i]);// Output array contents 
  }
  return 0;
}

The code executes as follows ：

summary ;1. Arrays are accessed using subscripts , The subscript is from 0 At the beginning .
2. The number of array elements can be calculated .
3. If the array is not initialized or assigned , Then garbage values may be stored in the array , It may also store 0, This stored result will be determined by the compiler .

One dimensional array storage in memory

Let's tap the code to observe the storage of one-dimensional arrays in memory （ Just find out here , You don't have to go into it , In the future, the study of pointer will be explained in detail ）

#include <stdio.h>
int main()
{
    
	int arr[10] = {
     0 };
	int i = 0;
	int sz = sizeof(arr) / sizeof(arr[0]);

	for (i = 0; i < sz; ++i)
	{
    
		printf("&arr[%d] = %p\n", i, &arr[i]);// Print the address of each element of the array in memory 
		//%p Is the address type 
	}
	return 0;
}

Pictured above , You can see the address of each element , This involves the binary problem , I suggest you know about various decimal conversions , It is helpful for future study .
As can be seen from the figure above , The address of each element of the array is adjacent , It can be concluded that ： Arrays are continuously stored in memory .

The creation and initialization of two-dimensional array

The creation of two-dimensional array

In fact, a two-dimensional array is a matrix in Mathematics , The code is shown as follows ：

int arr[3][4];//**3 That's ok 4 Two dimensional array of columns （ matrix ）**
char arr[3][5];//**3 That's ok 5 Two dimensional array of columns （ matrix ）**
double arr[2][4];//**2 That's ok 4 Two dimensional array of columns （ matrix ）**

Initialization of 2D array

int arr[3][4] = {
    1,2,3,4};
int arr[3][4] = {
    {
    1,2},{
    4,5}};
int arr[][4] = {
    {
    2,3},{
    4,5}};//** If the two-dimensional array is initialized , Lines can be omitted , Columns cannot be omitted **

The use of two-dimensional arrays

#include <stdio.h>
int main()
{
    
	int arr[3][4] = {
     0 };//** Two dimensional arrays are not fully initialized **
	int i = 0;
	for (i = 0; i < 3; i++)
	{
    
		int j = 0;
		for (j = 0; j < 4; j++)
		{
    
			arr[i][j] = i * 4 + j;//** Assign a value to a two-dimensional array **
		}
	}
	for (i = 0; i < 3; i++)
	{
    
		int j = 0;
		for (j = 0; j < 4; j++)
		{
    
			printf("%d ", arr[i][j]);//** Output the elements of a two-dimensional array **
		}
		printf("\n");
	}
	return 0;
}

The picture above shows 3 That's ok 4 Two dimensional array of columns （ matrix ）.

Two dimensional array storage in memory

Here we try to print the address of each element of the two-dimensional array .

#include <stdio.h>
int main()
{
    
	int arr[3][4];
	int i = 0;
	for (i = 0; i < 3; i++)
	{
    
		int j = 0;
		for (j = 0; j < 4; j++)
		{
    
			printf("&arr[%d][%d] = %p\n", i, j, &arr[i][j]);
		}
	}
	return 0;
}

Here, because it's just a print address , So there is no assignment to the two-dimensional array , Because when creating a two-dimensional array , Memory has been opened up . It can be seen from the above that the addresses of two-dimensional array elements are also continuous in memory .

An array

The subscript of an array is range limited .
The subscript of the array is specified from 0 At the beginning , If the array has n Elements , The subscript of the last element is n-1.
So if the subscript of the array is less than 0, Or greater than n-1, The array is accessed out of bounds , Access beyond the legal space of the array .
C The language itself does not check the bounds of array subscripts , The compiler does not necessarily report an error , But the compiler does not report an error , That doesn't mean the program is
That's right. ,
So when programmers write code , You'd better do cross-border inspection yourself .
The following is a code example ：

#include <stdio.h>
int main()
{
    
	int arr[10] = {
     1,2,3,4,5,6,7,8,9,10 };
	int i = 0;
	for (i = 0; i <= 10; i++)
	{
    
		printf("%d\n", arr[i]);//** When i be equal to 10 When , Cross border visit **
	}
	return 0;
}

Pictured above , The last string of numbers is usually called garbage value .

Arrays as function arguments

First, let's look at a set of code ：

#include <stdio.h>
int main()
{
    
	int arr[10] = {
     1,2,3,4,5 };
	printf("%p\n", arr);
	printf("%p\n", &arr[0]);
	printf("%d\n", *arr);// For the time being, let's understand * Is the value operator , It will be explained later when learning pointer 
	// Output results 
	return 0;
}

From the picture above, we can get , Array name is the address of the first element of the array , But there are two exceptions ：

int arr[10] = {
    0};
printf("%d\n", sizeof(arr));

The print out here is 40, So we can conclude that ：
1.sizeof（ Array name ） Will calculate the size of the entire array ,sizeof Put a separate array name inside , The array name represents the entire array .
2.& Array name , What we get is the address of the array ,& Array name , The array name represents the entire array .
In addition to the above two cases , All array names represent the address of the first element of the array .
We will take bubble sorting as an example , Here we first have a brief introduction , In the follow-up study of data structures and algorithms, we will explain in depth ,

As shown in the figure , Bubble sort is to sort an array in ascending or descending order , Every time I compare two , Compare until the last element of the array , If the array has n Elements can be compared at most n-1 Trip to , The following is a code example ：

#include <stdio.h>
void bubble_sort(int arr[], int sz)
{
    
	int i = 0;// Number of bubbling sortings 
	for (i = 0; i < sz-1; i++)
	{
    
		// Bubble sort 
		int j = 0;
		for (j = 0; j < sz-1-i; j++)
		{
    
			if (arr[j] > arr[j + 1])
			{
    
				int tmp = arr[j];
				arr[j] = arr[j + 1];
				arr[j + 1] = tmp;
			}
	    }
	}
}

int main()
{
    
	int arr[10] = {
    1,3,5,7,9,2,4,6,8,0};
	int sz = sizeof(arr) / sizeof(arr[0]);// Count the number of array elements 
	bubble_sort(arr, sz);// Passing an array as a parameter to a function requires only the array name 
	int i = 0;
	for (i = 0; i < sz; i++)
	{
    
		printf("%d ", arr[i]);
	}
	return 0;
}

When passing an array as shown in the above figure , Just pass in the array name , If Chuan arr[0] It means that the first element of the array is passed in instead of the entire array .
Add here , stay main The array created in function has no way to calculate the number of array elements and array size in other functions , So when taking an array as a function parameter , The number of array elements should also be transferred to the function .
The final production is not easy , Looking forward to your three consecutive and attention , You are welcome to write a private letter or point out what needs to be corrected in the comment area .