习题2.1 简单计算器（20 分）浙大版《数据结构（第2版）》题目集

import java.util.Scanner;

public class Main {

  public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int a = 0, b = 0;
    boolean flag = true;
    char ch = 0;
    String s;
    s = sc.nextLine();
    for(int i = 0;i < s.length();i ++)
    {
        if(s.charAt(i) >= ‘0‘ && s.charAt(i) <= ‘9‘)
        {
            b = s.charAt(i) - ‘0‘;
            while(s.charAt(i+1) >= ‘0‘ && s.charAt(i+1) <= ‘9‘)
            {
                i++;
                b *= 10;
                b += s.charAt(i) - ‘0‘;
            }
            if(ch == 0)a = b;
            else
            {
                if(ch == ‘+‘)a += b;
                else if(ch == ‘-‘)a -= b;
                else if(ch == ‘*‘)a *= b;
                else if(ch == ‘/‘)
                {
                    if(b == 0){flag = false; break;}
                    else a /= b;
                }
                else {flag = false;break;}
            }
        }
        else
        {
            if(s.charAt(i) == ‘=‘)break;
            ch = s.charAt(i);
        }
    }
    if(flag)System.out.print(a);
    else System.out.print("ERROR");
  }
}