How to cin to a vector

Question

I\'m trying to ask the user to enter numbers that are put into a vector, then using a function call to count the numbers, why is this not working? I am only able to count t

Answer 1

you have 2 options:

If you know the size of vector will be (in your case/example it's seems you know it):

vector<int> V(size)
for(int i =0;i<size;i++){
    cin>>V[i];
 }

if you don't and you can't get it in you'r program flow then:

int helper;
while(cin>>helper){
    V.push_back(helper);
}

Answer 2

The initial size() of V will be 0, while int n contains any random value because you don't initialize it.

V.size() < n is probably false.

Silly me missed the "Enter the amount of numbers you want to evaluate: "

If you enter a n that's smaller than V.size() at that time, the loop will terminate.

Answer 3

cin is delimited on space, so if you try to cin "1 2 3 4 5" into a single integer, your only going to be assigning 1 to the integer, a better option is to wrap your input and push_back in a loop, and have it test for a sentinel value, and on that sentinel value, call your write function. such as

int input;
cout << "Enter your numbers to be evaluated, and 10000 to quit: " << endl;
while(input != 10000) {
    cin >> input;
   V.push_back(input);
}
write_vector(V);

Answer 4

In this case your while loop will look like

int i = 0;
int a = 0;
while (i < n){
  cin >> a;
  V.push_back(a);
  ++i;
}

Answer 5

As is, you're only reading in a single integer and pushing it into your vector. Since you probably want to store several integers, you need a loop. E.g., replace

cin >> input;
V.push_back(input);

with

while (cin >> input)
    V.push_back(input);

What this does is continually pull in ints from cin for as long as there is input to grab; the loop continues until cin finds EOF or tries to input a non-integer value. The alternative is to use a sentinel value, though this prevents you from actually inputting that value. Ex:

while ((cin >> input) && input != 9999)
    V.push_back(input);

will read until you try to input 9999 (or any of the other states that render cin invalid), at which point the loop will terminate.

Answer 6

If you know the size of the vector you can do it like this:

#include <bits/stdc++.h>
using namespace std;

int main() {
    int n;
    cin >> n;
    vector<int> v(n);
    for (auto &it : v) {
        cin >> it;
    }
}