Fenwick

Debugging Help
#1

i was trying to solve this problem, and i did resolve it but there’s a thing that i don’t understand.
why this work:

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

struct Fenwick{
	vector<int> arr;
	int n;
	int last;
	void assign(int N){
		n=N+1;
		arr.resize(N+1,0);
		for(int i=1,i<N+1;i++){
			arr[i] = i & -i;
		}
		last = N;
	}
};

int main() {
	int T = 10;
	Fenwick fen;
	for(int i=0;i<T;i++){
		int N = i+1;
		fen.assign(N);
	}
}

and this one doesn’t:

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

struct Fenwick{
	vector<int> arr;
	int n;
	int last;
	Fenwick(int N) : n(N+1){
		arr.resize(N+1,0);
		for(int i=1,i<N+1;i++){
			arr[i] = i & -i;
		}
		last = N;
	}
};

int main() {
	int T=10;
	for(int i=0;i<T;i++){
		int N = i+1;
		Fenwick fen(N);
	}
}

when i say that “it works” i mean that it doesn’t crash, this is only a small part of the code but it’s the only difference between the two codes that i wrote for the problem.

#2

Both your programs don’t compile, but once I fix the for loop, it worked fine on my machine.