废话不多说，上代码：
myvec.h

#pragma once
#include <iostream>
#include <string>

using namespace std;

#define LENGTH	100

class myvec
{
public:
	myvec();
	~myvec();
private:
	int nCount;					//用于记录当前数组插入数据计数
	int nLen;					//数组实际长度
	int *arr;					//数组
	int *getmem();				//当数据
public:
	int insertVec(int data);	//插入
	int deleteVec();			//删除
	int updateVec(int pos);		//修改
	int at(int i);				//访问
	int nSize();
};

myvec.cpp

#include "myvec.h"

myvec::myvec()
{
	arr = new int[LENGTH]();
	nLen = LENGTH;
	nCount = 0;
}

myvec::~myvec()
{
	delete []arr;
	arr = NULL;
}

	
int *myvec::getmem()				//当数据
{
	if (nCount >= nLen / 2) {		//如果当数组实际插入数据已经到达数组长度的一半，就开始申请当前数组长度一半的数据
		nLen = nLen + nLen / 2;
		int* tmp = new int[nLen]();
		memcpy(tmp, arr, nCount*4);
		delete []arr;
		arr = tmp;
	}
	return arr;
}

int myvec::insertVec(int data)	//插入
{
	arr = getmem();
	arr[nCount++] = data;
	return 1;
}

int myvec::deleteVec()			//删除
{
	if (nCount < 1)
		return 0;
	arr[nCount] = 0;
	nCount--;
}

int myvec::updateVec(int pos)		//修改
{
	return 0;
}

int myvec::at(int i)				//访问
{
	if (i > nCount || i < 0)
		return 0;
	return arr[i - 1];
}

int myvec::nSize()
{
	return nCount;
}

main.cpp

#include "myvec.h"
int main()
{
	myvec vec;
	for (int i = 0; i < 40; i++)
		vec.insertVec(i);

	for (int i = 1; i <= vec.nSize(); i++){
		cout << vec.at(i) << " ";
		if (i % 10 == 0 && i > 0)
			cout << endl;
	}

	for (int i = 0; i < 80; i++)
		vec.insertVec(i + 40);

	for (int i = 1; i <= vec.nSize(); i++) {
		cout << vec.at(i) << " ";
		if (i % 10 == 0 && i > 0)
			cout << endl;
	}

	for (int i = 0; i < 30; i++) {
		vec.deleteVec();
	}
	cout << "------------------------------------------------------------------" << endl;
	for (int i = 1; i <= vec.nSize(); i++) {
		cout << vec.at(i) << " ";
		if (i % 10 == 0 && i > 0)
			cout << endl;
	}
	return 0;
}