Null pointer and wild pointer
1. Null pointer:
int * p = NULL;
[Pointing] : the space numbered 0
[Use] : initialized pointer variable
[Note] : ① null pointer memory is not accessible; ② 0-255 is the default memory space
2. Wild pointer:
int * p1 = (int*)0x1100;
Null pointers and wild pointers are not accessible
#include <iostream>
using namespace std;
int mian() {
//空指针
//指向 : 编号为0的空间
//用途 ：初始化的指针变量
//注意 : 空指针的内存是不可以访问的；0-255都是系统默认的内存空间
int* p = NULL;
//cout << *p << endl;//错误
//*p = 100;//错误
野指针
int* p1 = (int*)0x1100;
//cout << *p1 << endl;//错误
//空指针和野指针都是不能访问的
return 0;
}
const modified pointer
[ Memory method ]:
Whoever const follows, who can't change
const is called a constant , * is called a pointer
1. Constant pointer
-> Pointing can be changed, value cannot be changed
const int* p1 = &a;
p1 = &b;
cout << *p1 << endl;//输出20
2. Pointer constant
-> Pointing cannot be changed, value can be changed
int* const p2 = &a;
*p2 = 100;
cout << *p2 << endl;//输出100
3. Neither the pointing nor the value can be changed
const int* const p = &a;
#include <iostream>
using namespace std;
int main()
{
int a = 10;
int b = 20;
//常量指针->指向可改，值不可改
const int* p1 = &a;
p1 = &b;
cout << *p1 << endl;//输出20
//*p1 = 100; // const距离*最近，则取*的值不能改变
//指针常量->指向不可改，值可改
int* const p2 = &a;
//p2 = &b; // const距离p2最近，则取p2的值不能改变
*p2 = 100;
cout << *p2 << endl;//输出100
//都不能改
const int* const p = &a;
//记忆方法：const紧接着谁，谁就不能改变
//const叫做常量，*叫做指针
return 0;
}
Application of pointers and arrays
1、 *(p + i)
for (int i = 0; i < 10; i++)
{
cout << *(p + i) << endl;
}
2. *p and p++
for (int i = 0; i < 10; i++)
{
cout << *p << endl;
p++;
}
#include <iostream>
using namespace std;
int main()
{
//指针与数组
int arr[10] = {
1,2,3,4,5,6,7,8,9,10 };
int* p = arr;
cout << *p << endl;
for (int i = 0; i < 10; i++)
{
cout << *(p + i) << endl;
}
for (int i = 0; i < 10; i++)
{
cout << *p << endl;
p++;
}
return 0;
}
Application of pointers and functions
1. Value transfer
Can not change actual parameters through formal parameters
2. Address delivery
The actual parameters can be changed through the formal parameters
#include <iostream>
using namespace std;
//1.值传递函数
void swap01(int num1, int num2)
{
int temp = num1;
num1 = num2;
num2 = temp;
}
//2.地址传递函数
void swap02(int *p1,int *p2)
{
int temp = *p1;
*p1 = *p2;
*p2 = temp;
}
int main()
{
//函数与指针
int a = 10;
int b = 20;
//1.值传递
swap01(a, b);
cout << "a = " << a << "," << "b = " << b << endl;
//2.地址传递
swap02(&a, &b);
cout << "a = " << a << "," << "b = " << b << endl;
return 0;
}
Bubbling in ascending order (pointer)
Topic : Encapsulate a function and arrange the array in ascending order using bubble sorting
- Step 1: Create an array
- Step 2: Bubble function
- Step 3: Pass the address of the array, arr is the first address of the array
- Step 4: Output the array
#include <iostream>
using namespace std;
//封装一个函数，用冒泡排序法将数组升序排列
//第二步 ：冒泡函数
void bubbleSort(int* arr, int len)
{
for (int i = 0; i < len; i++)
{
for (int j = 0; j < len - i - 1; j++)
{
if (arr[j] > arr[j + 1])
{
int temp = arr[j];
arr[j] = arr[j + 1];
arr[j + 1] = temp;
}
}
}
}
//输出函数
void printArray(int *arr, int len)
{
for (int i = 0; i < len; i++)
{
cout << arr[i] << endl;
}
}
int main()
{
//第一步 ：创建一个数组
int arr[10] = {
2,5,6,3,4,7,1,9,24,13 };
int len = sizeof(arr) / sizeof(arr[0]);//数组长度
//第三步 ：传递数组的地址，arr就是数组的首地址
bubbleSort(arr, len);
//第四步 : 输出数组
printArray(arr, len);
return 0;
}