资深C ++程序员需要一些帮助

Question

 // rememb-o-matic
 #include <iostream>
 #include <new>
 using namespace std;

 int main ()

 {
   int i,n;
   int * p;
   cout << "How many numbers would you like to type? ";
   cin >> i;
   p= new (nothrow) int [i];
   if (p == 0)
     cout << "Error: memory could not be allocated";
   else
   {
     for (n=0; n<i; n++)
     {
       cout << "Enter number: ";
       cin >> p[n];
     }
     cout << "You have entered: ";
     for (n=0; n<i; n++)
       cout << p[n] << ", ";
     delete[] p;
   }
   return 0;
 }

Now,

why is their a bracket enclosed in variable i?

 p= new (nothrow) int [i];

why are their 2 for statements and what does a for statement do exactly?

Why is it deleting []p instead of the variable p ?

Answer 1

why is their a bracket enclosed in variable i? &
Why is it deleting []p instead of the variable p?

 p= new (nothrow) int [i];

Dynamically Allocates an int array of i elements .

 delete []p;

Deletes the dynamically allocated array.

---

Basic Rules of dynamic allocation in C++ are:

• If you use new to dynamically allocate memory, Use delete to deallocate it.
• If you use new [] to dynamically allocate memory, Use delete [] to deallocate it.

---

Also, note that you are using nothrow version of the new operator, it basically returns a null if some error condition and does not throw an exception, this allows the C++ code to be compatible with the legacy c code which uses null check after memory allocations(malloc returns null on failure).

---

what does a for statement do exactly?

A for statement is a conditional loop construct , It keeps on executing the loop untill the condition remains true. The basic syntax of for loop is:

for(;condition;)
{ 
    //doSomething
}

why are their 2 for statements?
The first for loop in your code gets the input from the user. It takes the input for i times.

The second for loop prints out the contents of the array.

---

Suggest you to pick up a good C++ book and read through the basics to understand more.

Answer 2

delete []表示您正在将数组释放回系统，if语句的无括号是可选的，仅表示如果为true，则将执行第一行，我认为您确实需要学习C ++和编程的一些基础知识总的来说，买一本好书或谷歌教程有很多好书

Answer 3

It is just C++ syntax.

1. new int [i] means that we want to allocate memory to store i integers.
2. delete [] p deletes memory bind to p. If [] are omitted, compiler assumes that p points to single instance of *p type. If instruction includes [] compiler tries to remove array of elements.