仿照vector手动实现自己的myVector，最主要实现二倍扩容功能

#include <iostream>

using namespace std;
class myvector
{
private:
    int *num;
    int size;
    int top=0;
public:
    //有参构造函数
    myvector(int s,int val)
    {
        int *tmp=new int [s];
        size=s;
        for(int i=0;i<s;i++)
        {
            tmp[i]=val;
            top++;
        }
        num=tmp;
    }
    //析构函数
    ~myvector()
    {
        delete [] num;
    }
    //展示函数
    void show()
    {
        for(int i=0;i<top;i++)
        {
            cout<<num[i]<<"   ";
        }
        cout<<endl;
    }
    //尾插
    void push_back(int val)
    {
        if(top==size)
        {
            size=size*2;
            int *tmp=new int[size];
            memcpy(tmp,num,sizeof(int)*size/2);
            num=tmp;
        }
        num[top]=val;
        top++;
    }
    int at(int a)
    {
        if(a<top)
        {
            return num[a];
        }else
        {
            return *num;
        }
    }
    //插入
    void inset(int s,int val)
    {
        if(top==size)
        {
            if(size==0)
            {
                size=2;
                int *tmp=new int[size];
                memcpy(tmp,num,sizeof(int)*size/2);
                num=tmp;
            }
            size=size*2;
            int *tmp=new int[size];
            memcpy(tmp,num,sizeof(int)*size/2);
            num=tmp;
        }
        for(int i=top;i>s;i--)
        {
            num[i]=num[i-1];
        }
        num[s]=val;
        top++;
    }
    //删除
    void dele(int s)
    {
        if(s<size)
        {
            for(int i=s;i<top-1;i++)
            {
                num[i]=num[i+1];
            }
            top--;
        }
    }
    //改
    void gai(int s,int val)
    {
        if(s<size)
        {
            num[s-1]=val;
        }
    }
    int back()
    {
        return num[top];
    }
    int *begin()
    {
        return num;
    }
    int capacity()
    {
        return size;
    }
    void claer()
    {
        top=size=0;
        delete []num; 
        num=nullptr;
    }
    int front()
    {
        return *num;
    }
    void pop_back()
    {
        top--;
    }
    int *end()
    {
        return num+top;
    }
    int ysdx()
    {
        return top;
    }
    void swap(int s,int n)
    {
        int tmp=num[s];
        num[s]=num[n];
        num[n]=tmp;
    }
};
int main()
{
    myvector a1(2,123);
    a1.push_back(199);
    a1.inset(3,1);
    a1.dele(3);
    a1.at(4);
    a1.gai(3,100);
    a1.show();
    return 0;
}