Printing the elements of vector

Question

In the following code, I have a 2D vector,in each index of vector each pair contains int and string. I am trying to access the each element after taking the values in the vector. Suggestions will be very much appreciated.

 #include <bits/stdc++.h>
 using namespace std;
 vector<pair<int,string>> aye[101];

int main()
{ int n,m,i,a,b;
  string x;
cin >> n >> m;
for (int i = 1; i <= n; ++i)
{
    cin >> x;
    cin >> a >> b;
    aye[a].push_back(make_pair(-b,x));
    cout<<aye[a].first<<aye[a].second;//this is not working
    cout<<aye[a][0]<<aye[a][1]<<endl;//this is not working

 }
}

didnt you ask a similar question some minutes ago? What is the error message? — 463035818_is_not_an_ai, May 10 '16 at 12:56
btw it still looks strange that you use an array of 100001 vectors, and still you should fix the most obvious errors first. You dont declare the variables. The first errors you will get is about `n` and `m` undeclared. Can`t you fix that? — 463035818_is_not_an_ai, May 10 '16 at 12:59
@tobi303 no one was giving the answer thats why i posted again..sorry for disturbance..i want to print the element stored in the vector — Shovo, May 10 '16 at 12:59
you could have edited the old question. There was no answer, because the question was not clear and because the code contained (and it still does) errors which let you not even reach the point of filling anything into the vector — 463035818_is_not_an_ai, May 10 '16 at 13:00
ok thats a bit better, but only a bit... what is the error message you get? — 463035818_is_not_an_ai, May 10 '16 at 13:01
@tobi303 sorry i was solving online judge problem and was in bit hurry to know the answer thats why i made those mistake... — Shovo, May 10 '16 at 13:03
if you try to do things fast it will take you (and also others) more time. If you take just some minutes to post real code and the error you are trying to fix, you might get an answer.... — 463035818_is_not_an_ai, May 10 '16 at 13:05
NathanOliver it was needed as,i was solving problem in the online judge.To solve that i needed that one — Shovo, May 10 '16 at 13:23
**Recommended reading: [Why should I not #include ?](http://stackoverflow.com/q/31816095/560648)** — Lightness Races in Orbit, May 10 '16 at 13:46
_"this is not working"_ is not an acceptable problem description. — Lightness Races in Orbit, May 10 '16 at 13:48

score 1 · Accepted Answer · answered May 10 '16 at 13:14

You seem to be confused by your 2d array structure (I have to admit, I am also a bit confused why you use something like that). This:

aye[a]

Is the (a+1)th element of the array, which is a vector, then

aye[a][i]

is the (i+1)th element in that vector, which is a pair and

aye[a][i].first
aye[a][i].second

are the first/second entries of that pair, respectively.

However, I have my doubts that you really need an array of vectors of pairs, especially as you seem to ignore one of the dimensions in the rest of the code.

Jonathan Mee · Answer 2 · 2016-05-10T13:34:04.370

You seem to be trying to print the element that you just added to the vector to do that, I'd suggest the use of vector::back. You could replace your two non-working lines with something like this:

cout << aye[a].back().first << ' ' << aye[a].back().second;

Live Example

Whatever your intent with this structure, the inputted values of a pose a threat to your design:

There is no check to see that thy fall between 0 and 100
You allocate 101 elements before even knowing n which means that 101 - n of these elements are wasted.

In this situation I believe using a map for your first dimension would be a far better plan; so you're structure would look like:

map<int, vector<pair<int, string>>> aye;

No further changes would need to be made to your code, but you would allocate only n vector<pair<int, string>>s whether n was larger or smaller than 101.

Printing the elements of vector

2 Answers2