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1. Creation and initialization of one-dimensional arrays
1.2 Initialization of the array
1.3 The use of one-dimensional arrays
1.4 Storage of one-dimensional arrays in memory
2. Creation and initialization of two-dimensional arrays
2.1 Creation of two-dimensional arrays
2.2 Initialization of two-dimensional arrays
2.3 The use of two-dimensional arrays
2.4 Storage of two-dimensional arrays in memory
3. Arrays as function parameters
1. Creation and initialization of one-dimensional arrays
1.1 Array creation
An array is a collection of elements of the same type .
How the array is created:
type_t arr_name [const_n];
//type_t 是指数组的元素类型
//const_n 是一个常量表达式，用来指定数组的大小Note: For array creation, before the C99 standard, a constant must be given in [ ], and a variable cannot be used. The concept of variable-length arrays is supported in the C99 standard.
Writing like this will throw an error:
//错误定义方式
int count = 10;
int arr2[count]; 1.2 Initialization of the array
The initialization of an array refers to giving some reasonable initial values (initialization) to the contents of the array while creating the array.
Note 1: incomplete initialization: the remaining elements are initialized to 0 by default
int arr1[10] = {1,2,3};
int arr2[10] = { 0 }; Note 2: When initializing, you can not specify the size of the array, the size of the array will be determined according to the number of elements in { }
int arr3[] = {1,2,3}; //数组大小为3 Note 3: Initialization of strings
#include <stdio.h>
#include <string.h>
char ch1[] = {'a', 'b', 'c', 'd'};
char ch2[] = "abcd";
printf("%d\n", sizeof(ch1)); //4
printf("%d\n", sizeof(ch2)); //5 '\0'也会被算进去
printf("%d\n", strlen(ch1)); //随机值，因为ch1中没有'\0'所以strlen会一直走，直到遇到'\0'为止
printf("%d\n", strlen(ch2)); //4ch1 stores abcd and ch2 stores abcd'\0'
1.3 The use of one-dimensional arrays
#include <stdio.h>
int main()
{
//数组的不完全初始化
int arr[10] = { 0 };
//计算数组的元素个数
int sz = sizeof(arr) / sizeof(arr[0]);
//对数组内容赋值,数组是使用下标来访问的，下标从0开始。所以：
int i = 0;//做下标
for (i = 0; i < sz; i++) //这里写10是不好的，当数组需要改动的时候这里需要跟着改，麻烦
{
arr[i] = i;
}
//输出数组的内容
for (i = 0; i < sz; ++i)
{
printf("%d ", arr[i]);
}
return 0;
}Summarize:
1. Arrays are accessed using subscripts, which start at 0.
2. The size of the array can be calculated.
1.4 Storage of one-dimensional arrays in memory
Observe the following code:
#include <stdio.h>
int main()
{
//数组的不完全初始化
int arr[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9};
//计算数组的元素个数
int sz = sizeof(arr) / sizeof(arr[0]);
int i;
//输出数组元素的地址
for (i = 0; i < sz; ++i)
{
printf("%p\n", &arr[i]);
}
return 0;
}The results are as follows:
It can be seen that as the index of the array grows, the address of the element also increases regularly - the address of adjacent elements differs by 4 bytes
Conclusion: One-dimensional arrays are stored contiguously in memory
Since it is stored contiguously in memory, all elements of the array can be accessed by the address of the first element :
#include <stdio.h>
int main()
{
int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
int* p = arr;
int i = 0;
for (i = 0; i < 10; i++)
{
printf("%d ", *p);
p++;
}
return 0;
}Note: The array name arr represents the address of the first element of the array
2. Creation and initialization of two-dimensional arrays
2.1 Creation of two-dimensional arrays
//数组创建
int arr[3][4]; //三行四列
char arr[3][5];
double arr[2][4];2.2 Initialization of two-dimensional arrays
//数组初始化
int arr[3][4] = {1,2,3,4}; //除第一行外全是0
int arr[3][4] = {
{ 1, 2},{ 3, 4},{ 5 }}; //1,2存入第一行 3,4存入第二行, 5存入第三行
int arr[][4] = {
{ 2, 3},{ 4, 5}}; //二维数组如果有初始化，行可以省略，列不能省略Note: If the two-dimensional array is initialized, the row can be omitted, and the column cannot be omitted
2.3 The use of two-dimensional arrays
#include <stdio.h>
int main()
{
int arr[3][4] = { { 1, 2 },{ 3, 4 },{ 5 } };
int i = 0;//行数
int j = 0;//列数
for (i = 0; i < 3; i++)
{
for (j = 0; j < 4; j++)
{
printf("%d ", arr[i][j]);
}
printf("\n");
}
return 0;
}2.4 Storage of two-dimensional arrays in memory
Print the address of each element in a two-dimensional array:
#include <stdio.h>
int main()
{
int arr[3][4] = { { 1, 2 },{ 3, 4 },{ 5 } };
int i = 0;//行数
int j = 0;//列数
for (i = 0; i < 3; i++)
{
for (j = 0; j < 4; j++)
{
printf("&arr[%d][%d] = %p\n", i, j, &arr[i][j]);
}
}
return 0;
}The results are as follows:
Conclusion: Two-dimensional arrays are also stored contiguously in memory
So you can also access two-dimensional array elements like this:
#include <stdio.h>
int main()
{
int arr[3][4] = { { 1, 2 },{ 3, 4 },{ 5 } };
int* p = &arr[0][0];
int i = 0;
for (i = 0; i < 12; i++)
{
printf("%d ", *p);
p++;
}
return 0;
}3. Arrays as function parameters
Array as a parameter actually uploads the address of the first element of the array
#include <stdio.h>
void bubble_sort(int* arr,int sz)
{
int i = 0;
for (i = 0; i < sz - 1; i++)
{
int j = 0;
for (j = 0; j < sz - 1 - i; j++) //10个元素，第一堂比较9次，第二趟比较8次以此类推
{
if (arr[j] > arr[j + 1])
{
int tmp = arr[j];
arr[j] = arr[j+1];
arr[j + 1] = tmp;
}
}
}
}
int main()
{
int arr[] = { 9, 8 ,7 ,6 ,5 ,4 ,3 ,2 ,1 ,0 };
//排序-排成升序
int sz = sizeof(arr) / sizeof(arr[0]);//为了确定排序的趟数：10个元素需要冒泡排序9趟
bubble_sort(arr,sz);//冒泡排序
int* p = &arr;
int i = 0;
for (i = 0; i < sz; i++)
{
printf("%d ", *p);
p++;
}
return 0;
}In the above code, if you calculate sz inside bubble_sort, you can see that sz is 1 after debugging, because the first element 4/first element 4=1
So the number of arrays should be calculated outside the function and passed in directly
Similarly, when passing parameters in a two-dimensional array, you need to pass in the number of rows and columns
What is the array name?
Answer: The array name is the address of the first element of the array (with two exceptions)
Exception 1. sizeof(array name), which calculates the size of the entire array.
Exception 2. & array name, the address of the array is taken out.