Vector resize

[funprogrammer]

Why does vector resize cause array entries to be zeroed out?

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


// It is NOT mandatory to use the provided template. You can handle the IO section differently.

int main() {
    /* The code required to enter n,k, candies is provided*/

    int N, K;
    cin >> N >> K;
    long long int temp;
    vector<long long int> numbers;
    numbers.resize(N);

    for (int i=0; i<N; i++){
        cin>>temp;
        cout<<"Temp is "<<temp<<endl;
        numbers.push_back(temp);        
    }
    for(int i=0;i<N;i++){
        cout<<numbers[i]<<endl;
    }
    cin.clear();

    long long int unfairness = 1000000;
    cout << unfairness << "\n";
    /** Write the solution code here. Compute the result, store in  the variable unfairness --
    and output it**/
    sort(numbers.begin(),numbers.end());
    for(int i=0;i<K;i++){
        cout<<numbers[i]<<endl;
    }
    
    for(int i=0; i<=N-K;i++){
       if((numbers[K+i-1]-numbers[i])<unfairness){
           unfairness=numbers[K+i-1]-numbers[i];
           cout << unfairness << "\n";
       }       
    }
    cout << unfairness << "\n";
    return 0;
}

If I comment/remove that line the contents of array is fine. What is wrong with using resize? When and how to use it?

[keskiverto]

There are two functions: resize() and reserve(). Read their descriptions.

[MiiNiPaa]

resize is changing logical size of container. If new size is less than current, some elements are deleted, if it is larger, some element are created and value-initialized. For integers it is 0.

So after line 17 you have vector without any elements. After line 18 you have vector with N zeroes. After push_back you have N zeroes and one number pushed.

What are you trying to do with resize here?