Suppose I've a vector as vector<int>a[n] and while compiling I give value of n as 2 . Can I keep on adding value to this array ?

Question

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

int main() {
/* Enter your code here. Read input from STDIN. Print output to STDOUT */
int n;
int q;
cin >> n >> q;
vector<int> a[n];
for(int i = 0; i < n; i++){
int m;
cin >> m;
int o;
for(int j = 0; j < m; j++){
cin >> o;
a[i].push_back(o);
}
}

int r, s;
for(int k = 1; k <= q; k++){
cin >> r >> s;
cout << a[r][s] << endl;
}
return 0;
}
Like in this code if i give n as 2 can I keep on adding values to the array if yes why?

Answer 1

Dreamer before you can add elements beyond the initial size you have to resize the vector. Here is more information:

https://www.geeksforgeeks.org/vector-resize-c-stl/

Answer 2

Dreamer,
I didn't clearly get the question. It might help if you can illustrate your intention, with an example ...

Answer 3

Okay let's see, first we make an array of <n> std::vector<int> we name it <a>.

Assuming <n> was 2 ...

a
{
std::vector<int>
std::vector<int>
}

Then we forge an inner loop where we read <m>, a number of elementa to be added to the std::vector element, identified by index <i> (defined in outer loop).

So here we are inserting <m> elements to the std::vector inside the array.

Is it clear now, it's fine if you have questions. I'll try to assist you as I can ...

Answer 4

Okay so when I compile this code I give input of value of n as 2 but as you can see in the first for loop it's repeating m times , let's the suppose the value of m as 4 then the for loop executes 4 times and adds values to the array 'a' ...assuming the elements to 5,6,7,8. But the array as defined in beginning was supposed to have 2 elements how is able to store 4 elements (5,6,7,8). I hope I cleared this question actually I'm not familiar with vectors.