what is the problem?

It was working fine on visual studio, but now it shows build error.

C++

else { vec3.at(i) = vec2.at(i); A Loop will run a 70 bool ispalindrome (const vector int>& vec) int i; 72 for (i = 0; i & vec, int x) { vec.pop_back(); 83 vec.push_back(x); } Initial size of veci Size of veci after i vec1 content: 5, 7, vec2 content: 4, 16