Vector programming problem.

[atreyucurses]

I need to be able enter two separate vectors. However, when i type in the entry 234 51 5125 Q, Q will continue to be read and the program will fail. How can i enter two separate vectors into data1 and data2?

vector<int> data1;
cout<<"Enter elements of first vector, Q to stop: ";
int input1;

while(cin>>input1)
{
data1.push_back(input1);
}


vector<int> data2;
cout<<"Enter elements of second vector, Q to stop: ";
int input2;
while(cin>>input2)
{
data2.push_back(input2);
}

[Duthomhas]

Press ENTER twice to finish:
http://www.cplusplus.com/forum/beginner/2409/#msg9254

Press ENTER once to finish:

#include <iostream>
#include <sstream>
#include <string>

...

vector <int> data1;
while (true)
  {
  cout << "Enter a list of integer numbers: ";
  string s;
  getline( cin, s );
  istringstream ss( s );
  int n;
  while (ss >> n)
    data1.push_back( n );

  if (ss.eof())
    break;
  else
    cerr << "Hey, element " << (data1.length() + 1) << " is not an integer number!\n";
  }

Hope this helps.

[atreyucurses]

I have to be able to enter two vectors of different length, i'm completely lost to the above example.
I need a way to clear the non integer value before the second while statement in my program. In order to enter a second set of vectors.

[S6k9GNh0]

#include <iostream>
#include <sstream>
#include <string>

vector <int> data1;
while (true)
  {
  cout << "Enter a list of integer numbers: ";
  string s;
  getline( cin, s ); //Places user input into string s;
  istringstream ss( s ); //Creates ss initiated to the string s.
  int n; 
  while (ss >> n) //This places the value of the string stream, into the integer.
    data1.push_back( n );

  if (ss.eof()) //If end of file, quit
    break;
  else //else here means that it isn't an integer and broke because ss >> n returned an error.
         //Generally not a good error message since it could be another reason as to why it failed.
    cerr << "Hey, element " << (data1.length() + 1) << " is not an integer number!\n";
  }

Although doesn't ss >> n fail if it contains spaces?

[Duthomhas]

Sigh. What I get for not compiling my own code first.

#include <iostream>
#include <sstream>
#include <string>
#include <vector>
using namespace std;

int main()
{
vector <int> data1;
while (true)
  {
  // I forgot this: make sure you start with a clean vector
  data1.clear();

  // Tell the user what you want:
  cout << "Enter a list of integer numbers: ";

  // Get the entire line at once
  string s;
  getline( cin, s );

  // Break the line up into individual int values using the >> operator
  istringstream ss( s );
  int n;
  while (ss >> n)
    data1.push_back( n );

  // Did we reach the end of the line (string) without any errors?
  if (ss.eof())
    // Yes! Great! We're done!
    break;
  else
    // Fooey! Tell the user to try again...
    cerr << "Hey, element " << (data1.size() + 1) << " is not an integer number!\n";
  }

// Reward the user for doing it right.
cout << "Good job! You entered:\n";
for (unsigned n = 0; n < data1.size(); n++)
  cout << data1[ n ] << endl;

cout << "Bye!\n";
return 0;
}

Try it and see what you can do to make it fail.

Line 29 explicitly tests to see if the stringstream terminated because of EOF and not some other error condition -- any other error condition will do. EOF is only signalled if the line parsed properly and completely into integer values.

Given this context, the only possible error that you can have is 'bad input': not an integer. The error message speaks precicely to that error, and even tells you where you went wrong.

(Though it could be off by one if you input something like 1 2.7 9 or 1 42rules! -3, a possibility I did not consider when typing this off the top of my head. As always, test code before you are done with it, so if this is an issue you can put in tests for separation between an error value and any previous element.)


Why would >> fail with spaces? It never does elsewhere (unless you explicitly use noskipws to tell it otherwise).


The nice feature about code like this is that it doesn't require all the flags and tests and other malarky necessary to deal with some oddball "marker"/"signal"/"semaphore" value. Instead it uses the marker value already given to us: the End Of Line (or "newline"). It decodes as many integers as it can out of a single line of text. When the line is exhausted, you have your complete list -- as many or as few elements as the user specified (including zero).


Hope this helps.