9、 C array explanation

One 、 Array basis

1.1 brief introduction

An array is an ordered collection of the same elements of a fixed size

1.2 Array declaration

• Format ：type array[array_size]
• give an example ：double array[10]

1.3 Initialize array ( use {} Represents an array )

• At initialization time , The number of elements in braces cannot be greater than the specified number of elements . If you omit the size of the array , The size of the array is the number of elements at initialization
• give an example ：
  • double array[2] = {1.1, 1.2}
  • double array[] = {1.1, 1.2, 1.3}

1.3 Array element assignment

• array[2] = 10 : Assign the third element of the array to 10

1.4 Practice

• Code implementation ：

  #include<stdio.h>
  
  int main(){
        
      int n[10];// Declare the number of elements as 10 The shape array of 
      int i;
      // Initialize array 
      for(i = 0;i < 10; i++){
        
          n[i] = i + 100;
      }
      // The output array 
      for(i = 0;i < 10; i++){
        
          printf(" Element value ：%d\n",n[i]);
      }
  }
  

• Running results ：

   Element value ：100
   Element value ：101
   Element value ：102
   Element value ：103
   Element value ：104
   Element value ：105
   Element value ：106
   Element value ：107
   Element value ：108
   Element value ：109
  

Two 、 Multidimensional arrays

2.1 Multidimensional arrays

• Format ：type array_name[size1][size2][size3]...;

2.2 Two dimensional array

• Format ：type array_name[ That's ok ][ Column ]

• Sort format ：
  

• Code implementation ：

  #include<stdio.h>
  
  int main(){
        
      int a[3][4] = {
        
          {
        0,1,2,3},
          {
        4,5,6,7},
          {
        8,9,10,11}
      };
      for(int i = 0; i < 3; i++){
        
          for(int j = 0; j < 4; j++){
        
              printf("a[%d][%d]=%d\n",i,j,a[i][j]);
          }
      }
      return 0;
  }
  

• Running results

  a[0][0]=0
  a[0][1]=1
  a[0][2]=2
  a[0][3]=3
  a[1][0]=4
  a[1][1]=5
  a[1][2]=6
  a[1][3]=7
  a[2][0]=8
  a[2][1]=9
  a[2][2]=10
  a[2][3]=11
  

2.3 A two-dimensional array stores strings , As a one-dimensional array

• Code implementation ：

  #include<stdio.h>
  
  int main(){
        
      // 2 Indicates the number of strings that can be stored 
      // 10 Represents the length of each string 
      char ch[2][10] = {
        " Zhang Fei "," zhaoyun "};
      printf("%s",ch[0]);
      return 0;
  }
  

• Running results ：

   Zhang Fei 
  

3、 ... and 、C Pass an array to a function

3.1 Pass a one-dimensional array as a function parameter

• Three ways of code implementation ：

  #include<stdio.h>
  /*  The way 1： The formal parameter is a pointer  void func(int *param){ } */
  void func1(int *array, int m){
        
      printf("func1**********\n");
      for(int i = 0; i < m; i++){
        
          printf("%d ",*(array + i));
      }
      printf("\n");
  }
  
  /*  The way 2： A formal argument is an array of defined sizes  void func(int array[3]){ } */
  void func2(int array[3], int m){
        
      printf("func2**********\n");
      for(int i = 0; i < m; i++){
        
          printf("%d ",array[i]);
      }
      printf("\n");
  }
  
  /*  The way 3： The formal argument is an array of undefined sizes  void func(int param[]){ } */
  void func3(int array[], int m){
        
      printf("func3**********\n");
      for(int i = 0; i < m; i++){
        
          printf("%d ",array[i]);
      }
      printf("\n");
  }
  int main(){
        
      int a[3] = {
        0,1,2};
      int m = sizeof(a) / sizeof(a[0]);
      func1(&a[0],3);
      func2(a,m);
      func3(a,m);
  }
  

• Running results ：

  func1**********
  0  1  2  
  func2**********
  0  1  2  
  func3**********
  0  1  2  
  

3.2 Pass a two-dimensional array as a function parameter

• Three implementation methods ：

  #include<stdio.h>
  /*  The way 1： The formal parameter is a pointer , Using arrays is the property of sequential storage  void func(int *param, m, n){ } */
  void func1(int *array, int m, int n){
        
      printf("func1**********\n");
      for(int i = 0; i < m; i++){
        
          for(int j = 0; j < n; j++){
        
              printf("%d ",*(array + i*n + j));//array Indicates the starting position of the array 
          }
          printf("\n");
      }
      printf("\n");
  }
  
  /*  The way 2： A formal argument is an array of defined sizes  void func(int (*a)[5],int m, int n){ } */
  void func2(int (*array)[3], int m, int n){
        
      printf("func2**********\n");
      for(int i = 0; i < m; i++){
        
          for(int j = 0; j < n; j++){
        
              printf("%d ",array[i][j]);//array Indicates the starting position of the array 
          }
          printf("\n");
      }
      printf("\n");
  }
  
  /*  The way 3： The parameters of the first dimension may not be specified , But the parameters of the second dimension must be specified  void func(int param[][5], int m, int n){ } */
  void func3(int array[][3], int m, int n){
        
      printf("func3**********\n");
      for(int i = 0; i < m; i++){
        
          for(int j = 0; j < n; j++){
        
              printf("%d ",array[i][j]);//array Indicates the starting position of the array 
          }
          printf("\n");
      }
      printf("\n");
  }
  int main(){
        
      int a[3][3] = {
        {
        1,2},{
        4,5,6},{
        7,8,9}};
      int m = sizeof(a) / sizeof(a[0]);
      func1(&a[0][0],3,3);
      func2(a,3,3);
      func3(a,3,3);
  }
  

• Running results ：

  func1**********
  1  2  0  
  4  5  6  
  7  8  9  
  
  func2**********
  1  2  0  
  4  5  6  
  7  8  9  
  
  func3**********
  1  2  0  
  4  5  6  
  7  8  9  
  

Four 、sizeof Application of function in array

• In the function , The array name represents an address pointing to the array
• Code implementation ：

  #include<stdio.h>
  
  void func1(int array[]){
        
      // sizeof What is returned is the memory size of an address , Not the memory size of the array 
      printf(" Inside the function sizeof(array) Value (int)：%ld\n",sizeof(array));
  }
  void func2(double array[]){
        
      printf(" Inside the function sizeof(array) Value (double)：%ld\n",sizeof(array));
  }
  
  void main(){
        
      int a[] = {
        1,2,3,4};
      double b[] = {
        1,2,3,4,5,6,7,8,9};
      int m = sizeof(a);
      int n = sizeof(a) / sizeof(a[0]);
      printf(" In the main function sizeof(array) Value ：%d\n",m);
      printf(" Array a Element number ：%d\n",n);
      func1(a);
      func2(b);
  }
  

• Running results ：

   In the main function sizeof(array) Value ：16
   Array a Element number ：4
   Inside the function sizeof(array) Value (int)：8
   Inside the function sizeof(array) Value (double)：8
  

5、 ... and 、 Address of array

5.1 The relationship between array value and array address

a[] = {
    1,2,3};

a: Represents the first address of the array , namely a[0] The address of 
a[0],a[1]： Represents the value 
a,(a+1),(a+2)： It represents the address 
(a+i)： representative a[0+i] The address of 

5.2 The difference between array assignment

char a[] = "xiao";// Will add... At the end '\0'
char a[] = {
    'x','i','a','o'};// Will not add '\0'
 therefore , The former is longer than the latter