2.0完美版

#include<iostream>
#include<cstdio> 
#include<stack> 
using namespace std;
stack<int>num;
int m,n,sum;
int main(){
    char ch;
    while(ch!='@'){
        ch=getchar();
        switch(ch){
            case'.':
                num.push(sum);
                sum=0;
                break;
            case'+':
                m=num.top();
                num.pop();
                n=num.top();
                num.pop();
                num.push(n+m);
                break;
            case'-':
                m=num.top();
                num.pop();
                n=num.top();
                num.pop();
                num.push(n-m);
                break;
            case'*':
                m=num.top();
                num.pop();
                n=num.top();
                num.pop();
                num.push(n*m);
                break;
            case'/':
                m=num.top();
                num.pop();
                n=num.top();
                num.pop();
                num.push(n/m);
                break;
            default:
                sum=sum*10+(ch-'0');
                break;
        }
    }
    cout<<num.top()<<endl;
    return 0;
}

#include <iostream>
#include <cstdio> 
#include <stack> 
using namespace std;
stack <int> num;
int m, n, sum;
int main() {
    char ch;
    while(ch != '@') {
        ch = getchar();
        switch(ch) {
            case '.':
                num.push(sum);
                sum = 0;
                break;
            case '+':
                m = num.top();
                num.pop();
                n = num.top();
                num.pop();
                num.push(n + m);
                break;
            case '-':
                m = num.top();
                num.pop();
                n = num.top();
                num.pop();
                num.push(n - m);
                break;
            case '*':
                m = num.top();
                num.pop();
                n = num.top();
                num.pop();
                num.push(n * m);
                break;
            case '/':
                m = num.top();
                num.pop();
                n = num.top();
                num.pop();
                num.push(n / m);
                break;
            default:
                sum = sum * 10 + (ch - '0');
                break;
        }
    }
    cout<<num.top()<<endl;
    return 0;
}

后缀表达式，经典模版题。

直接上代码！

#include<iostream> 
#include<cstdio>
#include<cstring>
#include<stack> 
using namespace std;
char s[1000];
int main(){
	gets(s);
	int n = strlen(s), x = 0, tmp;
	stack <int> a;
	for(int i = 0; i < n-1; i++)
	{
		switch(s[i]){
		case '.' :
			a.push(x);
			x = 0;
			break;
		case '+' : 
			tmp = a.top(); a.pop();
			a.top() += tmp;
			break;
		case '-' :
			tmp = a.top(); a.pop();
			a.top() -= tmp;
			break;
		case '*' :
			tmp = a.top(); a.pop();
			a.top() *= tmp;
			break;
		case '/' :
			tmp = a.top(); a.pop();
			a.top() /= tmp;
			break;
		default:
			x = x * 10 + s[i] - '0';
		}
	}
	printf("%d", a.top());
	return 0;
}

https://www.luogu.com.cn/record/78364318

（本人完隐，看不到记录）