表达式求值-栈的应用

版权声明： https://blog.csdn.net/jtjljy/article/details/82880554

自己练练手，写了个栈用来进行表达式求值。

记录一下~（用‘#’表示开始结束~）

不过可能也存在着一些问题，就是用double存整数可能会出现问题,另外异常处理还没有完善。

还存在很大优化空间。

#include <iostream>
#include <sys/malloc.h>
//win上为malloc.h
#include <cmath>

using namespace std;

typedef int Status;
#define OK 0
#define ERROR -1
#define ET double

struct node{
    //int stacksize;
    ET data;
    node * next;
};
struct stack{
    node * base;
    node * top;
};

typedef node* Node;
typedef stack* Stack;

Stack init(){
    Stack head=(Stack) malloc(sizeof(stack));
    Node n= (Node)malloc(sizeof(node));
    head->base=n;
    head->top=head->base;
    return head;
}


Status Insert(Stack head,ET x)
{
    head->top->data=x;
    if(head->top==head->base)
    {
        head->top->next=NULL;
    }
    Node n=(Node)malloc(sizeof(node));
    n->next=head->top;
    head->top=n;
    return OK;
}

ET Pop_Node(Stack head)
{
    if(head->top==NULL)
        return ERROR;
    ET tmp=head->top->next->data;
    head->top=head->top->next;
    return tmp;
}

int rules[7][7]={
        1,1,0,0,0,1,1,
        1,1,0,0,0,1,1,
        1,1,1,1,0,1,1,
        1,1,1,1,0,1,1,
        0,0,0,0,0,-1,-2,
        1,1,1,1,-2,1,1,
        0,0,0,0,0,-2,-1
};//-1相等，0小于，1大于，-2无

/*
 * 0 +
 * 1 -
 * 2 *
 * 3 /
 * 4 (
 * 5 )
 * 6 #
 */

int char_to_int(ET c)
{
    switch (int(c)){
        case '+':
            return 0;
        case '-':
            return 1;
        case '*':
            return 2;
        case '/':
            return 3;
        case '(':
            return 4;
        case ')':
            return 5;
        case '#':
            return 6;
        default:
            return -1;
    }


}


Status Check(ET c1,ET c2)
{
    int c_1=char_to_int(c1);
    int c_2=char_to_int(c2);
    return rules[c_1][c_2];
}


int main() {
    Stack head_num = init();
    Stack head_char = init();
    Insert(head_char,'#');
    char c[1000];
    //char tmp_c[10];
    cout<<"===表达式求值-1.0 CS1702 Kingtous==="<<endl;
    cout<<"请输入你要计算的表达式：";
    cin.getline(c, sizeof(c));
    int pos=0;
    for (;c[pos]!='\0';++pos);
    c[pos]='#';
    //cin.getline(tmp_c, sizeof(tmp_c));
    for (int i=0;c[i]!='\0';++i)
    {
        int p=-1;
        bool isPoint=false;
        if(c[i]<='9' && c[i]>='0')
        {
            double total=c[i]-'0';
            while((c[i+1]>='0' && c[i+1]<='9')|| c[i+1]=='.')
            {
                if(c[i+1]=='.')
                {
                    isPoint= true;
                    i++;
                }
                i++;
                if(isPoint)
                {
                    total=total+(c[i]-'0')*pow(10,p);
                    p--;
                }
                else
                    total=total*10+(c[i]-'0');
            }
            Insert(head_num,total);
        }
        else
        {
            isPoint=true;//reset
            p=-1;//reset
            //-1相等，0小于，1大于，-2无
            check_again:
            switch ( Check(head_char->top->next->data,c[i]) )
            {
                case 0:
                    Insert(head_char,c[i]);
                    break;
                case -1:
                    Pop_Node(head_char);
                    break;
                case 1:
                    double num1=Pop_Node(head_num);
                    double num2=Pop_Node(head_num);
                    char ch= int(Pop_Node(head_char));
                    switch (ch)
                    {
                        case '+':
                            Insert(head_num,num2+num1);
                            break;
                        case '-':
                            Insert(head_num,num2-num1);
                            break;
                        case '*':
                            Insert(head_num,num2*num1);
                            break;
                        case '/':
                            Insert(head_num,num2/num1);
                            break;
                    }
                    goto check_again;
            }
        }
    }
    cout<<"表达式 = "<<Pop_Node(head_num)<<endl;
    return 0;

}