牛客网真题2019-31-加减法解析

import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        int p = 0;
        int sum = 0;
        String flag = "";
        String number = "0";
        for(int i = 0; i < s.length(); i++){
            switch (s.charAt(i)) {
                case '-':
                    sum += Integer.parseInt(flag + number);
                    flag = "-";
                    number = "";
                    break;
                case '+':
                    sum += Integer.parseInt(flag + number);
                    flag = "";
                    number = "";
                    break;
                default:
                    number += s.charAt(i);
            }
        }
        sum += Integer.parseInt(flag + number);
        System.out.println(sum);
    }
}