Article directory
1. Array
1.1 Why do we need arrays
1. In order to solve the storage and use problems of a large amount of data of the same type
2. To simulate the real world
1.2 Classification of arrays
There are three types of arrays:
1、一维数组
2、二维数组
3、多维数组
1.3 One-dimensional array
1.3.1 Defining arrays
1、为n个变量连续分配存储空间。
2、所有的变量数据类型必须相同
3、所有变量所占的字节大小必须相等
1.3.1.2 Basic operation
1.3.1.2.1 Initialization
- fully initialized
int a[5] = {
1, 2, 3, 4, 5}; //在定义数组时就完全赋值
- Incomplete initialization, uninitialized elements are automatically zero
int a[5] = {
1, 2, 3};// 在定义数组时部分值初始化
- Not initialized, the values of all elements are uncertain, all are garbage values
int a[5];
- array of zeros
int a[5] = {
0}; // 所有的元素都为零
- Only when the array is defined can the overall assignment be made, in other cases the overall assignment is wrong
int a[5] = {
1, 2, 3, 4, 5};
- Initializing a Read-Only Array
Sometimes it is necessary to make an array read-only, in which case values can only be retrieved from the array, and new values cannot be written to the array. To create such an array, the array should be declared and initialized with the const keyword.
// 使用const关键字声明后，该数组就只能读，不能修改
const char ch[5]={
1, 2, 3, 4, 5};
1.3.1.2.2 Find
The lookup of the array is carried out according to the subscript index, and the index starts from 0.
#include <stdio.h>
int main(){
// 定义一个数组
char ch[5]={
11, 21, 22, 33, 44};
// 取出数组的第2个值，因为索引是从0开始，ch[1]表示取出数组的第二个值。
printf("%d", ch[1]); // 返回21
return 0;
}
When you need to take out all the values of the array, you need to use a loop to take out all the values
#include <stdio.h>
int main(){
//定义数组
char ch[5]={
11, 21, 22, 33, 44};
// 定义自增变量
int i;
// for循环取值
for(i=0; i<5; i++){
printf("%d\n", ch[i]);
}
return 0;
}
To retrieve all the character arrays, you can use the strlen() function to calculate the length of the array.
#include <stdio.h>
// 使用strlen函数需要引用此头文件
#include <string.h>
int main(){
//定义字符数组
char arr[]={
'a', 'b', 'c', 'd'};
// 自增变量
int i;
// 循环取出字符数组的值。strlen计算arr数组的长度，但索引从0开始，需要减1
for(i=0; i<strlen(arr)-1; i++){
printf("%c\n", arr[i]);
}
return 0;
}
1.3.1.2.3 Assignment
After declaring an array, you can use the array subscript (or index) to assign values to elements. You can directly assign a value to the subscript of the element to be modified by assignment.
#include <stdio.h>
#include <string.h>
int main(){
char arr[]={
'a', 'b', 'c', 'd'};
int i;
// 将arr数组的第2个元素修成'e'
arr[1] = 'e';
for(i=0; i<strlen(arr)-1; i++){
printf("%c\n", arr[i]);
}
return 0;
}
1.3.1.2.4 Array Copy
In the C language, one array cannot be directly assigned to another array. Need to traverse the loop to assign to another array.
int a[5] = {
1, 2, 3, 4, 5};
int b[5];
//如果要把a数组中的值全部复制给b数组
Wrong way:
b = a //error
Correct spelling:
for (i = 0; i < 5; ++i)
b[i] = a[i]
1.3.1.2.5 Array Sorting
Here is a simple counterfeit sort first, and will continue to explain in detail later
# include <stdio.h>
// 冒泡排序函数
void bubble_sort(int arr[], int len){
int i, j;
int temp=0;
for(i=0;i<len;i++){
for (j = 0; j<len-i-1; j++){
if (arr[j] > arr[j+1]){
temp=arr[j];
arr[j]= arr[j+1];
arr[j+1]=temp;
}
}
}
}
// 主函数
int main(void){
int i;
int arr[]={
5, 2, 7, 6, 9, 3, 4, 12, 10};
int len = sizeof(arr)/sizeof(int);
//
bubble_sort(arr, len);
for (i = 0; i < len; i++)
{
printf("%d\n", arr[i]);
}
return 0;
}
1.4 Two-dimensional array
A two-dimensional array represents rows and columns. The following example represents a two-dimensional array with 3 rows and 4 columns. When a two-dimensional array is stored in memory, it is stored in a continuous memory space.
int a[3][4]; //总共有12个元素，可以当作3行4列看待。a[i][j]表示第i+1行第J+1列的元素
1.4.1 Initialization
A two-dimensional array, like a one-dimensional array, also has full initialization and incomplete initialization. Uninitialized values are zero when not fully initialized.
Full initialization method one:
int a[3][4] = {
1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
Full initialization method two:
int a[3][4] = {
{
1, 2, 3, 4},
{
5, 6, 7, 8},
{
9, 10, 11, 12}
};
Incomplete initialization:
// 不完全初始化，后面的8个元素全为0
int arr[3][4]={
1, 2, 3, 4}
1、在初始化时，行可以省略，但列不能省略。
2、初始化时建议使用方式二的方式初始化。
1.4.2 Basic Operation
1.4.2.1 Outputting the contents of an array
# include <stdio.h>
int main(void)
{
int a[3][4] = {
{
1, 2, 3, 4},
{
5, 6, 7, 8},
{
9, 10, 11, 12}
};
int i, j;
for (i = 0; i < 3; ++i)
{
for (j = 0; j < 4; ++j)
printf("%-5d ",a[i][j]); //-5表示左对齐五个字符。
printf("\n");
}
return 0;
}
1.5 Multidimensional arrays
1. Is there a multi-dimensional array
? No, because the memory is linearly unique, and an n-dimensional array can be regarded as a one-dimensional array in which each element is an n-1-dimensional array.
for example:
int a[3][4]
It can be regarded as a one-dimensional array with each element containing 4 small elements.
int a[3][4][5]
The array contains a one-dimensional array of 3 elements, but each element is a two-dimensional array of 4 rows and 5 columns.