Runtime error(beginner)

#include
int main()
{ int t;
std::cin>>t;
while(t–)
{
int n;
std::cin>>n;
int a[n];int i;
while(n>0)
{
a[i]=(n%10);
n/=10;
++i;
}
std::cout<<a[0]+a[i-1];
}
return 0;
}
The problem is FLOW004. What should I do to avoid runtime error?

Initialize i=0 before starting loop, otherwise the array goes out of bounds.

Please read this thread it might help you get better responses in the future.

at the the time of declration of i,initialise with i=0; otherwise loop will never end.