Recognition of C language array

 

 

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Catalog

1. One dimensional array creation and initialization

1.1 Array creation

1.2 Initialization of an array

1.3 The use of one-dimensional arrays

1.4 One dimensional array storage in memory

2. The creation and initialization of two-dimensional array

2.1 The creation of two-dimensional array

2.2 Initialization of 2D array

2.3 The use of two-dimensional arrays

2.4 Two dimensional array storage in memory

3. An array

4. Arrays as function arguments

4.1 Wrong design of bubble sort function

4.2 What is the array name ？

4.3 Correct design of bubble sorting function

5. Array instance ：

5.1 Application examples of arrays 1： Sanzi

5.2 Application examples of arrays 2： The Minesweeper game

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  Let's start today's recognition of arrays ！

 

1. One dimensional array creation and initialization

1.1 Array creation

An array is a collection of elements of the same type .
How to create an array ：

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 

  An instance created by an array ：

// Code 1
int arr1[10];
// Code 2
int count = 10;
int arr2[count];// Arrays can be created normally ？
// Code 3
char arr3[10];
float arr4[1];
double arr5[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 the concept of variable length arrays .

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 ）.
Look at the code ：

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 to distinguish , How to allocate in memory .

char arr1[] = "abc";
char arr2[3] = {'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;
}

summary :
1. Arrays are accessed using subscripts , The subscript is from 0 Start .
2. The size of the array can be calculated .
 

int arr[10];
int sz = sizeof(arr)/sizeof(arr[0]);

1.4 One dimensional array storage in memory

Next, we discuss the storage of arrays in memory .
Look at the code ：
 

#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;
}

  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 .

 

2. The creation and initialization of 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 Initialization of 2D array

// 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 The use of two-dimensional arrays

Two dimensional arrays are also used by subscripts .
Look at the code ：

#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 in memory

Like a one-dimensional array , Here we try to print each element of a 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;
}

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

3. 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 .

#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;
}

Rows and columns of two-dimensional arrays may also be out of bounds .

4. Arrays as function arguments

4.1 Wrong design of bubble sort function

Often when we write code , Will pass the array as an argument to a function , such as ： I want to implement a bubble sort （ Here is the idea of algorithm ） The function sorts an integer array .

Then we will use this function ：

// Method 1：
#include <stdio.h>
void bubble_sort(int arr[])
{
int sz = sizeof(arr)/sizeof(arr[0]);// Is that right ？
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 i=0;
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;
}

Method 1, have a problem , Let's find a problem , After debugging, you can see bubble_sort intra-function sz , yes 1.
When an array is used as a function parameter , Instead of passing the entire array ？

4.2 What is the array name ？

#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 array name is the address of the first element of the array （ In general ）

If the array name is the first element address , that ：

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

Why the output is ：40？
Add ：
1. sizeof( Array name ), 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 this 1,2 Except for two cases , All array names represent the address of the first element of the array . 

4.3 Correct design of bubble sorting function

When an array passes parameters , In fact, it just passes the address of the first element of the array .
So even if it is written as an array in the parameter part of the function ： int arr[] It still represents a pointer ： int *arr .
that , intra-function sizeof(arr) The result is 4.
If Method 1 In the wrong , How to design ？

// Method 2
void bubble_sort(int arr[], int sz)// Parameter to receive the number of array elements 
{

	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 i=0;
int arr[] = {3,1,7,5,8,9,0,2,4,6};
int sz = sizeof(arr)/sizeof(arr[0]);
bubble_sort(arr, sz);// Whether it can be sorted normally ？
for(i=0; i<sz; i++)
{
printf("%d ", arr[i]);
}
return 0;
}

 

5. Array instance ：

5.1 Application examples of arrays 1： Sanzi

5.2 Application examples of arrays 2： The Minesweeper game
 

These two examples will be explained in detail in a special topic later , Hope not to miss it ！！！

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