char[] cNum = sNum.toCharArray()
String을 Char 배열로 변환
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int N = sc.nextInt();
String sNum = sc.next();
char[] cNum = sNum.toCharArray();
int sum = 0;
for (int i = 0; i < cNum.length; i++) {
sum += cNum[i] - '0';
}
System.out.println(sum);
}
}