import java.util.Scanner; public class Main{ public static void main(String []args){ Scanner sc = new Scanner(System.in); while(sc.hasNext()){ int n = sc.nextInt(); int index = -1; int [] arr = new int [n]; for(int i = 0; i < n; i++){ arr[i] = sc.nextInt(); } int goalNum = sc.nextInt(); for(int j = 0; j < n; j++){ if(goalNum == arr[j]){ index = j; break; } } if(index >= 0){ System.out.printf("%d\n",index); }else{ System.out.printf("No\n"); } } } }可以先使下标为-1,因为没有-1的下标,在将数字存入数组,在查找数字,有的话就返还下标结束循环。