흠 start = mid는 에러나는 군

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

string board;

int main() {
	cin >> board;
	// #####____
	int len = 10;
	if (board[0] == '_') {
		cout << "0%";
	}
	else if (board[len - 1] == '#') {
		cout << "100%";
	}
	else {
		int start = 0;
		int end = len - 1;
		while (1) {
			int mid = (start + end) / 2;
			if (board[mid - 1] == '#' && board[mid] == '_') {
				cout << mid << "0%";
				break;
			}
			else if (board[mid - 1] == '#') {
				start = mid+1;
			}
			else {
				end = mid - 1;
			}
		}
	}


}

start = mid라고 설정하니까

에러 뜸;;;