中綴轉後綴+後綴求值（數值可以是小數類型和超過一位的整數）

 nyoj  http://nyoj.top/problem/267

#include <cstdio>
#include <queue>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <math.h>
#include <map>
#include <vector>
#include <set>
#include<stdlib.h>//atof函數頭文件
#include <bitset>
#include <stack>
#define ull unsigned long long
#define mems(a,b) memset(a,b,sizeof(a))
#define inf 0x3f3f3f3f
using namespace std;
typedef long long ll;
const ll mod=100000007;
const double pi=acos(-1);
stack<char>op;
stack<double>q;
char s[1100],s1[1100],s2[1110];
int priority(char ch)
{
    if(ch=='(')
        return 1;
    else if(ch=='+'||ch=='-')
        return 2;
    else if(ch=='*'||ch=='/')
        return 3;
    return -1;
}
int main()
{
    int t;
    scanf("%d",&t);
    op.push('#');
    while(t--)
    {
        scanf("%s",s1);
        int len=strlen(s1);
        int p=-1;
        for(int i=0;i<len;i++)////中綴轉後綴，從前向後掃；前綴是從後向前掃
        {
            if((s1[i]>='0'&&s1[i]<='9')||s1[i]=='.')
            {
                s2[++p]=s1[i];
            }
            else if(s1[i]=='+'||s1[i]=='-'||s1[i]=='*'||s1[i]=='/')
            {
                if(priority(s1[i])>priority(op.top()))//優先級大於棧頂優先級
                {                                     //前綴是大於等於
                    s2[++p]=' ';
                    op.push(s1[i]);
                }
                else
                {
                    while(priority(s1[i])<=priority(op.top()))//優先級小於等於棧頂
                    {                                         //前綴是小於
                        s2[++p]=' ';
                        s2[++p]=op.top();
                        op.pop();
                    }
                    s2[++p]=' ';
                    op.push(s1[i]);
                }
            }
            else if(s1[i]=='(')
            {
                s2[++p]=' ';
                op.push(s1[i]);
            }
            else if(s1[i]==')')
            {
                while(op.top()!='(')
                {
                    s2[++p]=' ';
                    s2[++p]=op.top();
                    op.pop();
                }
                s2[++p]=' ';
                op.pop();
            }
        }
        while(op.top()!='#')
        {
            s2[++p]=' ';
            s2[++p]=op.top();
            op.pop();
        }
        for(int i=0;i<=p;i++)
        {
            if(s2[i]!=' ')//註釋此行可以明確看到大於等於十和小於十的數是怎麼存到s2裏的
                printf("%c",s2[i]);
        }
        printf("=\n");
        int f=-1;int k=0;
        for(int i=0;i<=p;i++)
        {
            if((s2[i]>='0'&&s2[i]<='9')||s2[i]=='.')
            {
                s[k++]=s2[i];
                f=1;
                continue;
            }
            if(f==1)
            {
                s[k]='\0';
                double c1;
                c1=atof(s);
                q.push(c1);
                f=-1;k=0;
            }
            else if(s2[i]==' ')
                continue;
            else if(s2[i]=='+'||s2[i]=='-'||s2[i]=='*'||s2[i]=='/')
            {
                double b,a1,a2;
                a1=q.top();q.pop();
                a2=q.top();q.pop();
                if(s2[i]=='+')
                {
                    b=a1+a2;
                    q.push(b);
                }
                if(s2[i]=='-')
                {
                    b=a2-a1;
                    q.push(b);
                }
                if(s2[i]=='*')
                {
                    b=a1*a2;
                    q.push(b);
                }
                if(s2[i]=='/')
                {
                    b=a2/a1;
                    q.push(b);
                }
            }
        }
        printf("%.2lf\n",q.top());
        printf("\n");
    }
    return 0;
}
 
/*
3
1+(3+2)*(7^2+6*9)/(2)
(6*2)^0/2
6*2^0/2
*/