Catalog

One 、 One dimensional array

1.1 Array creation

1.2 Initialization of an array

1.3 The use of one-dimensional arrays

1.4 Storage of one-dimensional array in memory

Two 、 Two dimensional array

         2.1 The creation of two-dimensional array

2.2 2D array initialization

2.3 Two dimensional arrays use

2.4 Two dimensional array storage

3、 ... and 、 An array

Four 、 Arrays as arguments to functions

         4.1 Bubble sort （ error ）

4.2 Array name

4.3 Bubble sort （ correct ）

One 、 One dimensional array

1.1 Array creation

An array is a collection of elements of the same type ;

Array creation

​
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 an array 


int arr1[10];
char arr2[10];
float arr3[1];
double arr4[20];

​

notes ： Array creation , stay C99 Before standard , [ ] You have to give a constant in the , You can't use variables . stay C99 The standard supports variable length numbers The concept of group , The size of the array can be specified by variables , But arrays cannot be initialized .

1.2 Initialization of an array

The initialization of an array refers to , While creating an array, give the contents of the array some reasonable initial values （ initialization ）.

for example ：

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 you want to create an array without specifying the size of the array, you have to initialize it . The number of elements in the array is determined according to the contents of initialization .

But for the following code ：

char arr1[] = "abc";
char arr2[3] = {'a','b','c'};

Although the character array is initialized to abc , But arrays 1 During initialization, there are actually 4 Elements , Respectively "a" "b" "c" "\0" , And arrays 2 There are three elements in “a" "b" "c" .

1.3 The use of one-dimensional arrays

For the use of arrays, we introduced an operator ： [] , Subscript reference operator . It's actually an array access operator . So let's look at the code ：

#include <stdio.h>
int main()
{
 int arr[10] = {0};// Incomplete initialization of arrays 
    // Count the number of elements in an array 
    int sz = sizeof(arr)/sizeof(arr[0]);
 // Assign values to the contents of the array , Arrays are accessed using subscripts , Subscript from 0 Start . therefore ：
 int i = 0;// Do subscripts 
 for(i=0; i<10; i++)// Write here 10, Ok or not ？
 {
 arr[i] = i;
 }
 // Output the contents of the array 
 for(i=0; i<10; ++i)
 {
 printf("%d ", arr[i]);
 }
 return 0;
}

The output of this code is ：0 1 2 3 4 5 6 7 8 9

summary : 1. Arrays are accessed using subscripts , The subscript is from 0 Start .

         2. The size of the array can be calculated .

1.4 Storage of one-dimensional array in memory

We can check the address of the array through the code , as follows ：

#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]);
 }
 return 0;
}

The operation results are as follows ：

Watch the output carefully , We know , As the array subscript grows , Address of element , It's also increasing regularly . So we can draw a conclusion ： Arrays are continuously stored in memory . 

Two 、 Two dimensional array

2.1 The creation of two-dimensional array

// Array creation 
int arr[3][4];
char arr[3][5];
double arr[2][4];

2.2 2D array initialization

// Array initialization 
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 

2.3 Two dimensional arrays use

Similar to one-dimensional array , Two dimensional arrays are also accessed through subscripts

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

2.4 Two dimensional array storage

#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;
}

The operation results are as follows ：

  Through the results, we can analyze , In fact, two-dimensional arrays are also stored continuously in memory .

3、 ... and 、 An array

The subscript of an array is range limited .

The next stipulation of the array is 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 right , So when programmers write code , You'd better do cross-border inspection yourself

Four 、 Arrays as arguments to functions

4.1 Bubble sort （ error ）

Often when we write code , Will pass the array as an argument to a function , such as ： I want to implement a bubble sort function Sort an integer array .

#include <stdio.h>
void bubble_sort(int arr[])
{
 int sz = sizeof(arr)/sizeof(arr[0]);
    int i = 0;
 for(i=0; i<sz-1; i++)
   {
        int j = 0;
        for(j=0; j<sz-i-1; j++)
       {
            if(arr[j] > arr[j+1])
           {
                int tmp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = tmp;
           }
       }
   }
}
int main()
{
    int arr[] = {3,1,7,5,8,9,0,2,4,6};
    bubble_sort(arr);// Whether it can be sorted normally ？
    for(i=0; i<sizeof(arr)/sizeof(arr[0]); i++)
   {
        printf("%d ", arr[i]);
   }
    return 0;
}

actually , This code cannot realize bubble sorting , Why? ？

Through debugging, we can find that inside the function , We can calculate sz=1, Here we will mention the transfer method of array as a function parameter .

4.2 Array name

Let's start with a piece 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);
    // Output results 
    return 0;
}

The result is ：

We can come to a conclusion ：

The array name is the address of the first element  

however , We also use the array name when calculating the size of the array , It seems that the array size can be output normally .

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

The result is ：40

notes ：

1. sizeof( Array name ), Calculate the size of the entire array ,sizeof Put a separate array name inside , At this point, 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 this 1,2 Except for two cases , All array names represent the address of the first element of the array

4.3 Bubble sort （ correct ）

Now let's write the correct bubble sort code ：

void bubble_sort(int arr[], int sz)// Parameter to receive the number of array elements 
{
 for(i=0; i<sz-1; i++)
   {
        int j = 0;
        for(j=0; j<sz-i-1; j++)
       {
            if(arr[j] > arr[j+1])
           {
                int tmp = arr[j];
                arr[j] = arr[j+1];
                arr[j+1] = tmp;
           }
       }
   }
}
int main()
{
    int arr[] = {3,1,7,5,8,9,0,2,4,6};
    int sz = sizeof(arr)/sizeof(arr[0]);
    bubble_sort(arr, sz);
    for(i=0; i<sz; i++)
   {
        printf("%d ", arr[i]);
   }
    return 0;
}