while(cin >>x) terminates program

[mellish]

I have just started learning C++. Every time I use a while (cin>>x) loop, when the loop is terminated no other input is accepted.

Please can someone explain why this is.

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main()
{
	vector<int> vec;
	int x;
	int sum = 0;
	cout << "Please enter the numbers: \n\n";
	while (cin>>x){
		vec.push_back(x);
	}
	for (int i = 0; i != vec.size(); ++i){
		cout << vec[i] << ' ' ;}
	int numtosum;
	cout << "How many numbers would you like to sum? \n\n";
	cin >> numtosum;
}

I enter an invalid character say '|' to exit the while loop, but this seems to print the next line and exit the program. No prompt is shown to input the next value.

Thanks for any help.

[mordekai]

It is because of the way cin works:

1. It ignores whitespaces (space, tab, newline)
2. It reads Input to the next whitespace
3. It leaves the whitespace in the buffer

So, if you type "| <Enter>" the newline character is still in the buffer, is read by "cin >> numtosum;" and the program exits. So, either you type
cin.ignore(1000,'\n')
before cin >> numtosum;

or you use getline() (i would recommend this)

Here is more information about getline() and user input
http://www.cplusplus.com/forum/articles/6046/

[mellish]

Thanks for the reply.

cin.ignore doesn't wok either I just get the same result.

Can you use getline() in a while loop?

and is getline not just for strings?

[maros522]

cin.ignore(1000,EOF)
1000 - means in how long stream will be the EOF ignored

[maros522]

and for the getline, you can try it and you will see

[mellish]

Still no joy with cin.ignore(1000,EOF)

I'm putting it before the cin >> numtosum line. I'm getting the same result as before.

I'm working through the new Stroustrup book and this is the way he says to do it. This is why I am surprised it doesn't work.

[Zhuge]

Maybe you should also use cin.clear() since inputting invalid data puts cin into an error state.

[Zaita]

while(getline(cin, input)) {
 // do stuff with input
}

is perfectly valid.