了解使用"new int[]"的目的

#include "stdafx.h"
using namespace std;
#include <iostream>
#include<conio.h>
#include<stdio.h>
#include<stdlib.h>
#include<time.h>
using namespace std;
//Search program
 void read_data(int* , int); //array address, size
int seq_search(int , int* , int);//key,array address,size
int binary_search(int , int* , int);
void main(void)
{
int  *arr , size , ans , key ;
cout << "Please enter the size: ";
cin >> size ;
arr = new int[size] ;
read_data(arr , size);
cout << "Enter the number to search for: ";
cin >> key ;
ans = binary_search(key, arr , size);
if(ans == -1)   
    cout << "The number " << key << " does not exist n";
else    
    cout << "The number " << key << " exists at location " << ans << endl;
getch();
}
void read_data(int *pt , int ss)
{
cout << "Please enter " << ss << " numbers: n";
for(int k = 0 ; k < ss ; k++)
{
    cout << "Enter the " << k + 1 << " number: " ;
    cin >> pt[k] ;
}
}
int seq_search(int num , int a[] , int s)
{
for(int k = 0 ; k < s ; k++)
    if(num == a[k])     { return k ; }
return -1 ;
}
int binary_search(int num , int a[] , int s)
{
int first , last , mid ;
first = 0 ;     last = s -1 ;
while(first <= last)
{
    mid = (first + last) / 2 ;
    if(num == a[mid])               return mid ;
    else if(num > a[mid])       first = mid + 1 ;
    else                                    
last   = mid - 1 ;
}
return -1;
}

从我的理解(我是一个真正的初学者)是，例如* p = a;指向地址如果整数a，并且p = %a;是a的引用地址或实际地址。

我理解我们使用这个新的int是为了在程序的任何地方使用数组，因为它在main结束时被销毁，但是为什么我不在main之外声明它也可以在任何地方使用呢?