Question about string & character array

I see this in the guidelines of my assignment. It is rather confusing.

Code:

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char arr[10];
cin.getline(arr,10);
string str(arr);

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Beside the use of string function, what is the point of converting the content of a character array into string?
Why use character array?Why not just define a string?

I can't think of any reason, besides not knowing about the non-member getline function.

Perhaps the intent is to limit the input to 9 characters. The string version of getline is not capable of doing that.

Thx!
I need to convert part of a character array into integer and am wondering how.
How to convert string into integer ?
How to convert string into content of a character array ?

I ask these questions because I think the atoi thing on C++.com may be able to do these. It need an entire character array but in my case, I only need part of a character array for conversion to integer.
This is the example on c++.com:

Code:

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/* atoi example */
#include <stdio.h>
#include <stdlib.h>

int main ()
{
  int i;
  char szInput [256];
  printf ("Enter a number: ");
  gets ( szInput );
  i = atoi (szInput);
  printf ("Value entered is %d, and its double %d",i,i*2);
  return 0;
}

Output:
Enter a number: 73
Value entered is 73, and its double 146

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More basic question about string. My problem is here:

Code:

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#include <iostream>
#include <stdlib.h>
#include <string>
using namespace std;
void main()
{
        string str='000-000-0000';//The compiler said the string is too long. How to fix it?
        if (str=='000-000-0000')//Using == operator is illegal here. How to fix it?
        cout<<str;
}

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Single quotes/apostrophes (' ') denote a single char, double quotes(" ") a char array; use double quotes.

Also, use int main, not void main. Also, prefer cstdlib over stdlib.h and only if your code requires it.

Thank you, Ken.