简单来说，就是弄两个栈，判断执行：

上代码： 

#include<iostream>
#include<stack>
#include<cstring>
using namespace std;
stack<char>s1,s2;
char now;
int main(){string c;cin>>c;for(int i=0;i<c.length();i++){if(c[i]>='0'&&c[i]<='9'){s2.push(c[i]);if(!(c[i+1]>='0'&&c[i+1]<='9'))s2.push('.');	} else if(c[i]=='+'||c[i]=='-'){while(!s1.empty()&&s1.top()!='('){s2.push(s1.top());s1.pop();}s1.push(c[i]);}else if(c[i]=='*'||c[i]=='/'){while(!s1.empty()&&(s1.top()=='*'||s1.top()=='/')){s2.push(s1.top());s1.pop();}s1.push(c[i]);}else if(c[i]=='('){s1.push(c[i]);}else if(c[i]==')'){while(s1.top()!='('){s2.push(s1.top());s1.pop();}s1.pop();}}while(!s1.empty()){s2.push(s1.top());s1.pop();}while(!s2.empty()){s1.push(s2.top());s2.pop();}while(!s1.empty()){cout<<s1.top();s1.pop();}return 0;
}

因为csp中常考的就是中、后缀的计算，所以先写这些，后续再更