Issues with default for an int

[Ascendant78]

Ok, I am a newcomer to C++ and running into an issue. I am using the introductory book by Stroustrup and attempting some basic code with int that I am running into a problem with. According to the book, the code below should cause the output to give a result of "-1" for the age if no integer is entered (for example, if I enter '22 Carlos'). While the string outputs fine, the int gives me a value of 0 if no int is entered. I have entered everything exactly as they stated in the book, so can someone please tell me where I'm going wrong?

  #include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<cmath>
using namespace std;
inline void keep_window_open() {char ch; cin>>ch;}
//  The above code uses the standard library directly, eliminating the need for the std_lib_facilities.h

int main ()
{
    cout << "Please enter your first name and age (followed by 'enter'):\n";
    string first_name = "???" ;   //  first name is a variable of type string, default is "???"
    int age = -1;  // age is a variable of type int, default is "-1"
    cin >> first_name;   // places input from user into the string variable
    cin >> age;    // places input from user into the int variable
    cout << "Hello, " << first_name << ", age " << age << "!\n";
}

[JLBorges]

> According to the book, the code below should cause the output to give a result of
> "-1" for the age if no integer is entered ... I have entered everything exactly as they
> stated in the book, so can someone please tell me where I'm going wrong?

You have not gone wrong anywhere.
A new version of the International Standard for C++ (C++11) was published after the book was written.

Before C++11, the behaviour was as stated in the book; on input failure, the value of age would not be changed; age would continue to hold the previous value of -1

Since C++11, on input failure, the value of age would be set to zero.

You are using an implementation that conforms to the current standard.

[Duthomhas]

What?! I didn't know that! That's stupid!
If there is no value to assign to an object, why assign anything at all?
I'll definitely have to read up on the rationale for that...

[Ascendant78]

Well thank you for that information. I'll have to look around for other changes made by that new version. I am at a bit of a loss though as to why they made a change like that, but then again I am new to all this, so sure there must be some good reasoning behind it.

[TheToaster]

Yes, the new C++11 standard changes this behavior. I would suggest looking at more recent books that teach C++11, such as this one:

http://www.amazon.com/Programmers-Edition-Deitel-Developer-Series/dp/0133439852

good luck!

[Duthomhas]

It's a significant change. Perhaps I should add a FAQ on it. If JL will allow, I'll just use his words (nearly) verbatim.

[JLBorges]

Something like this perhaps:

If extraction fails, failbit is set and the value stored in the numeric variable is:
a. Zero if no part of the input could be converted (eg. if "hello" was entered where a number was expcted).
b. The largest representable positive value if the input represents a value that would have been larger.
c. The largest representable negative value (or zero for unsigned integer types) if the input represents a value that would have been smaller.