1-2 24:00 (20 points) [CSP certification true question]

Define each game by 4 From the 1-9 And 3 It consists of four operators , Make sure that the four operators separate numbers , There are no brackets and other characters , The order of operation follows the order of four operations . In addition, the sign + Express , Subtraction uses the symbol - Express , Multiplication in small letters x Express , Divide with the sign / Express . In the game, division is called integral division , for example 2 / 3 = 0,3 / 2 = 1, 4 / 2 = 2. The teacher gave you n The solution to the game , Please write a program to verify whether the result of each game is 24 .

Input format :

Reading data from standard input . Enter an integer in the first line n, From 2 OK, we're going to start with n + 1 In line , Each line contains a length of 7 String , For the above 24 Click game , Make sure the data format is legal .

Output format :

Output to standard output . contain n That's ok , For every game , If the result is 24 Then the output string Yes, Otherwise output string No.

Examples "> Examples "> Examples "> sample input :

10
9+3+4x3
5+4x5x5
7-9-9+8
5x6/5x4
3+5+7+9
1x1+9-9
1x9-5/9
8/5+6x9
6x7-3x6
6x4+4/5

sample output :

Yes
No
No
Yes
Yes
No
No
No
Yes
Yes

This topic is mainly Consider the priority of the four operations . But I don't know the right conventional way of thinking , Just think for yourself , It turned out to be stuck bug, I spent the whole afternoon looking for bug Spend in .....

Own code ：（.. No comments at all. Hahaha , Don't look at this ..

  Problems in my thinking , Record as a reminder .

#include <iostream>
#include<cmath>
#include<algorithm>
#include<iomanip>
#include<vector>
#include<string>
#include<cstring>
#include<map>
#include<stack>
using namespace std;
int sum ;


int main()
{
	int n;
	cin >> n;// Number of formulas 
	cin.get();
	char ch;
	stack<char> zhan1;// Originally, I thought that operators and numbers should be used char To express , The numbers are just -‘0’, That's all right. , but 
	stack<int>zhan2;  // forget char Type can only represent 0-9 Array of , When it is a two digit number , One digit will be lost .
	for (int i = 0; i < n; i++)
	{
		sum = 0;
		int j = 0;
		while (true)  
		{
			
			for (; j < 7; ) // Here I was while（(ch=cin.get()!='\n'), I thought I could finish reading "enter" 
			{
				ch = cin.get();                Very good , But it's actually out of circulation , But when the outer loop executes 
				if ((ch >= '0'&&ch <= '9'))    Next time , Because there is the next expression , So I began to receive 
				{                             cin>>ch; But the current formula is not finished yet , card bug, I also read it 
					zhan2.push(ch - 48);       For a long time ...
					
				}
				else
				{
					if ((ch == '+') || ch == '-')
					{
						zhan1.push(ch);
						
					}
					else
					{
						int a = zhan2.top();
						zhan2.pop();
						char b;
						b = cin.get();
						j++;
						int c = b - 48;
						if (ch == '/')// Here I used the time *, But the reality is ×, The question is , Both are not 
						{             // equally , I've been reporting mistakes all the time , If you use the division sign in the future, it will be ÷ Also pay attention to , can 
							a = a / c;// You can find the corresponding decimal number , As a basis for judgment .
						}
						else
						{
							a = a *c;
						}
						zhan2.push(a);
					}
				}
				j++;
			}
			int re;
			if (zhan2.size()==1&&zhan1.size()==0)
			{
				
				sum = zhan2.top();
				zhan2.pop();
				if (sum < 0)
					sum = 0 - sum;
				break;
			}
			int a = zhan2.top();
			zhan2.pop();
			int c = zhan2.top();
			zhan2.pop();
			char b = zhan1.top();
			zhan1.pop();
			if (b == '+')// Here is what I found in the data given in the experimental topic , When I'm doing calculations , I didn't pay attention to the sequence of operations 
				re = a + c;// Sequential , Advanced stack in front , The last one in the stack is at the back .
			else
				re = a - c;
			zhan2.push(re);
		}
		if (sum == 24)
			cout << "Yes" << endl;
		else
			cout << "No" << endl;
		getchar();

	}
	return 0;
				
}

The right way of thinking ： First, for numbers and operators , Use it separately char The type and int Type of stack To store , Because if it is stored only by inserting ,char It can only mean 0~9; So when the result is two digits , One will be lost , I watched it for a long time .  Mainly for operator priority analysis ： At the top of the stack （* 、/）> Received （*、/）> At the top of the stack （+、-）> Received （+、-）. Such priority operations are constantly compared with the operators of the operation stack , For example, receive as +, The priority of the operator at the top of the stack is lower than that of the operator at the top of the stack , Then let the operation at the top of the stack , At the same time, the top of the stack element pops up , After taking part in the calculation , Again, compare with the new stack top element in the pop-up stack , Until the operation participates in the operation or is pushed onto the stack .                                                                           

At the same time, we can also analyze , Such a priority , The operators in the stack cannot exist at the same time （+ -） And （* /） Of .

Thought code ：

It can be noted that ：num1,num2 There is a sequence of operations , The last one in the stack is at the back , First in first .