" Abort signal from abort(3) (SIGABRT)" . Why only for some cases?

Question

I am trying to form largest number from elements of array. My implementation given below is working fine for some cases and for some other its giving error " Abort signal from abort(3) (SIGABRT)" . Why? Help me out!

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

int main() {
int t;
cin>>t;
while((t--)>0){
    int n;
    cin>>n;
    int a[n];
    string s="";
    for(int i=0;i<n;i++){
        cin>>a[i];
        if(i==0){s+=to_string(a[i]); continue;}
        string s1 = s+to_string(a[i]); //sX
        string s2 = to_string(a[i])+s; //Xs

        if(stoi(s1)>=stoi(s2))s=s1;
        else s = s2;
    }
    cout<<s<<endl;
    }

return 0;
 } 

For the following case my code is giving the error

4                  //size of array
54 546 548 60      //elements of array

Answer 1

This is due to the stoi function. This does not work with a very large number.
For a string to int conversion try the following approach.

Algorithm to manually converting a string to int:

int x = 0; // may take long long 
for(int i = 0; i < s.length(); i++)
    x = x * 10 + s[i] - '0';

Variable x will store the integer value of the string in discussion.