C/C++ Intro to c++ help with vector problem

[medonaldson2]

So I'm trying to do this problem:

Write a for loop to populate vector userGuesses with NUM_GUESSES integers. Read integers using cin. Ex: If NUM_GUESSES is 3 and user enters 9 5 2, then userGuesses is {9, 5, 2}.

Here is my code so far...

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

int main() {
   const int NUM_GUESSES = 3;
   vector<int> userGuesses(NUM_GUESSES);
   int i = 0;
   
   for (i = 0; i < NUM_GUESSES; i++) {
      cin >> userGuesses[i];
   }
   cout << userGuesses[i];

   return 0;
}

The output is when tested with values {2, 4, 6}

02 4 6

The output needs to be...

2 4 6

I don't know why the zero is there. Any ideas?

thanks

 

[Greg]

I managed to get the desired output with

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

int main() {
		const int NUM_GUESSES = 3;
		vector<int> userGuesses(NUM_GUESSES);
		int i;

		for (i = 0; i < NUM_GUESSES; i++) {
			cin >> userGuesses[i];
		}

		cout << '\n';

		for (i = 0; i < NUM_GUESSES; i++) {
			cout << userGuesses[i] << ' ';
		}

		cout << '\n';

		return 0;
}

I made some minor changes. Hopefully you can spot them. :)

 

[johng1]

The problem with your code is at the line:

cout<<userGuesses[i];

When this is executed, the value of i is 3!. But userGuesses has components at 0, 1 and 2. There is no component v[3]. The standard says (I looked it up) that this causes no run time error, but the result could be any thing. The member function at of vector, userGuesses.at(i), has the same behavior as [], but will "throw an exception" since there is no such component of userGuesses. The exception causes immediate exit from the program. So when using a vector, it is up to the programmer to ensure any reference using [] is a valid component of the vector.

greg1313 has shown you a correct program. Notice he uses a loop to output the contents of userGuesses. You can not write cout<<userGuesses; i.e. cout does not accept vectors to output.