中缀表达式计算

首先把中缀表达式转为后缀表达式，

1+4*2

如图所示，你需要准备两个栈，左边的栈用来装后缀表达式，右边的栈用来装运算符。

运算符进入左边栈的规则如下，

低进制见高进制时，立即反应。

比如+-一出现就把右边已有的全部进栈，自己独待右栈。

如果*号出现，并且前边紧贴着^，那么^也要出栈。但不pop 其他的。

置于括号，左括号没感觉，右括号出现的时候，把两括号夹着的运算符赶入栈。

就这样就行了。

#include <iostream>
#include <math.h>
using namespace std;
struct num_strT{
    int num;
    char s;
    bool status;//status ==0 represent s, else num;
};
class screenC{
    //用于接受后缀表达式
    public:
    int total,status;
    num_strT what_on_screen[30];
    void insert(char symbol)
    {
        what_on_screen[total].s=symbol;
        what_on_screen[total].status=0;
        total++;
    }
    void insert(int n)
    {
        what_on_screen[total].num=n;
        what_on_screen[total].status=1;
        total++;
    }
    void print()
    {
        for(int i=0;i<total;i++){
            if(what_on_screen[i].status==0)
            {
                cout<<what_on_screen[i].s;
            }
            else
            {
                cout<<what_on_screen[i].num;
            }
        }
    }
};
class zhanC{
    public:
    char zhan[30];
    int total;
    int num_of_brace;
    void push(char symbol)
    {
        zhan[total]=symbol;
        total+=1;
        if(symbol=='(')num_of_brace++;
    }
    char pop()
    {
        total-=1;
        return zhan[total];
    }
};
class answer_zhanC{
    public:
    int zhan[30];
    int total;
    void push(float n)
    {
        zhan[total]=n;
        total+=1;
    }
    int pop()
    {
        total-=1;
        return zhan[total];
    }
};
int main(){
    screenC screen;
    zhanC zhan;
    answer_zhanC answer;
    screen.total=0;
    zhan.total=0;
    answer.total=0;
    zhan.num_of_brace=0;
    char s[26],*p;
    int temp,brace_left=0,brace_right=0;
    int a,b;
    bool button_minus,button_minusnum;
    cin>>s;
    p=s;
    while(*p)
    {
        if(*p=='(')brace_left+=1;
        else if(*p==')')brace_right+=1;
        p++;
    }
    if(brace_left!=brace_right)
    {
        cout<<"Error";
        return 0;
    }
    p=s;
    while(*p!='\0')
    {
        //*P 1, + - * / ( )
        if(*p>='0' &&*p<='9')
        {
            temp=0;
            while(*p>='0'&&*p<='9')
            {
                temp=temp*10+*p-'0';
                p++;
            }
            button_minus=false;
            if(button_minusnum==true){button_minusnum=false;temp=-temp;}
            screen.insert(temp);
        }
        else if(*p=='+'||*p=='-')
        {
            if(*p=='+')button_minus=true;
            if(*p=='-'&&button_minus==true)
            {
                button_minusnum=true;
                button_minus=false;
            }
            else{
            if(zhan.num_of_brace==0)
            {
                while(zhan.total!=0)
                {
                    screen.insert(zhan.pop());
                }
            }
            zhan.push(*p);
            }
            p++;
        }
        else if(*p=='*'||*p=='/'||*p=='(')
        {
            if(*p!='('&&zhan.zhan[zhan.total-1]=='^')
                {
                    screen.insert(zhan.pop());
                }
            if(*p=='/'&&zhan.zhan[zhan.total-1]=='*')
                {
                    screen.insert(zhan.pop());
                }
            button_minus=true;
            zhan.push(*p);
            p++;
        }
        else if(*p==')')
        {
            button_minus=false;
            char the_last_pop=zhan.pop();
            while(the_last_pop!='(')
              {
                  screen.insert(the_last_pop);
                  the_last_pop=zhan.pop();
              }
            zhan.num_of_brace-=1;
            p++;
        }
        else if(*p=='^')
        {
            button_minus=true;
            zhan.push(*p);
            p++;
        }
    }
    while(zhan.total!=0)
        {
            screen.insert(zhan.pop());
        }

    for(int i=0;i<screen.total;i++)
    {
        if(screen.what_on_screen[i].status==1)
        {
            //此时为数字
            answer.push(screen.what_on_screen[i].num);
        }
        else
        {
            //此时为字符
            switch(screen.what_on_screen[i].s)
            {
                case '+':b=answer.pop();a=answer.pop();answer.push(a+b);break;
                case '-':b=answer.pop();a=answer.pop();answer.push(a-b);break;
                case '*':b=answer.pop();a=answer.pop();answer.push(a*b);break;
                case '/':b=answer.pop();a=answer.pop();if(b!=0){answer.push(a/b);}else{cout<<"Error";return 0;}break;
                case '^':b=answer.pop();a=answer.pop();answer.push(pow(a,b));break;
            }
        }
    }
    cout<<int(answer.pop());
}