Finding next palindrome of a number, getting SIGABRT error - c++

Question

Hi ,I am trying to solve the question PALIN on SPOJ where the idea is to find the next immediate palindrome of a number. I tested my code on the IDE with all possible test cases I found and the program is working fine but I can't figure out why I am getting SIGABRT error when I submit the solution.Please I request someone help me figure out the problem in the code For yor reference I am providing the link of the question:- https://www.spoj.com/problems/PALIN/
#include<iostream>
#include<stdio.h>
#include<vector>
#include<string>
using namespace std;
bool all_nines(string s)
{
for(int i=0;i<s.length();i++)
{
if(s[i]!='9')
return false;
}
return true;
}
int reverse(int a)
{
int rev=0;
while(a)
{
rev=(rev*10)+(a%10);
a/=10;
}
return rev;
}
void convert_and_compare(string &s,int low,int high)
{
int low_num,high_num;
string low_str="",high_str="";
for(int i=0,j=high;i<=low,j<s.size();i++,j++)
{
low_str+=s[i];
high_str+=s[j];
}
low_num=stoi(low_str);
high_num=stoi(high_str);
if(reverse(low_num)<=high_num)
{
low_num++;
low_str=to_string(low_num);
high_str="";
for(int i=low_str.length()-1;i>=0;i--)
high_str+=low_str[i];
}
else
{
high_str="";
for(int i=low_str.length()-1;i>=0;i--)
high_str+=low_str[i];
}
s="";
s+=low_str+high_str;
}
void convert_and_compare(string &s,int low,int high,int mid)
{
int low_num,high_num,mid_num;
string low_str="",high_str="";
char mid_str;
for(int i=0,j=high;i<=low,j<s.size();i++,j++)
{
low_str+=s[i];
high_str+=s[j];
}
low_num=stoi(low_str);
high_num=stoi(high_str);
mid_num=(s[mid]-'0');
if(reverse(low_num)>high_num)
{
low_str=to_string(low_num);
high_str="";
for(int i=low_str.length()-1;i>=0;i--)
high_str+=low_str[i];
mid_str=mid_num+'0';
}
else if(reverse(low_num)<=high_num && mid_num!=9)
{
mid_num++;
high_str="";
for(int i=low_str.length()-1;i>=0;i--)
high_str+=low_str[i];
mid_str=mid_num+'0';
}
else if(reverse(low_num)<=high_num && mid_num==9)
{
mid_num=0;
low_num++;
low_str=to_string(low_num);
high_str="";
for(int i=low_str.length()-1;i>=0;i--)
high_str+=low_str[i];
mid_str=mid_num+'0';
}
s="";
s=low_str+mid_str+high_str;
}
string find_next_palin(string s)
{
if(all_nines(s))
{
s[0]='1';
for(int i=1;i<s.length();i++)
s[i]='0';
s+='1';
return s;
}
else
{
if(s.length()%2==0)
{
int low,high;
low=s.length()/2-1;
high=s.length()/2;
convert_and_compare(s,low,high);
return s;
}
else
{
int low,high,mid;
mid=s.length()/2;
low=mid-1;
high=mid+1;
convert_and_compare(s,low,high,mid);
return s;
}
}
}
int main()
{
int t;
scanf("%d",&t);
vector <string> v(t);
for(int i=0;i<t;i++)
{
cin>>v[i];
}
for(int i=0;i<t;i++)
{
if(v[i].length()==1)
{
if(v[i]=="9")
{ printf("11");
printf("\n");
}
else
{
printf("%d",(v[i][0]-'0')+1);
printf("\n");
}
}
else
{
string temp;
temp=find_next_palin(v[i]);
for(int j=0;j<temp.length();j++)
cout<<temp[j];
printf("\n");
}
}
return 0;
}