字符串算术表达式运算-逆波兰解法

/*

*转自百度百科代码

*/

思路：用到两个栈S1,S2,S1存放表达式逆波兰表示的结果，S2临时栈存放运算符。

#include<iostream>

#include<stdlib.h>

#include<stdio.h>

#include<stack>

#include<math.h>

#include <string.h>

#define max 100

using namespace std;

char ex[max]; /*存储后缀表达式*/

 

void trans()

{ /*将算术表达式转化为后缀表达式*/

    char str[max]; /*存储原算术表达式*/

    char stack[max]; /*作为栈使用*/

    char ch;

    int sum,i,j,t,top=0;

    printf("*****************************************\n");

    printf("*输入一个求值的表达式，以#结束。*\n");

    printf("******************************************\n");

    printf("算数表达式：");

    i=0; /*获取用户输入的表达式*/

    do{

        i++;

        //cin>>str[i];/*此步我用的是C++ C语言的话在后面 之所以用这个有一点区别 都*/

        scanf("%c",&str[i]);

      }while(str[i]!='#' && i!=max);

    sum=i;

    t=1;i=1;

    ch=str[i];i++;

//

    while(ch!='#')

    {

        switch(ch)

        {

            case '(': /*判定为左括号*/

                top++;stack[top]=ch;

                break;

            case ')': /*判定为右括号*/

                while(stack[top]!='(')

                {

                    ex[t]=stack[top];top--;t++;

                }

                top--;

                break;

            case '+': /*判定为加减号*/

            case '-':

                while(top!=0&&stack[top]!='(')

                {

                    ex[t]=stack[top];

                    top--;

                    t++;

                }

                top++;

                stack[top]=ch;

                break;

            case '*': /*判定为乘除号*/

            case '/':

                while(stack[top]=='*'||stack[top]=='/')

                {

                    ex[t]=stack[top];

                    top--;

                    t++;

                }

                top++;

                stack[top]=ch;

                break;

            case ' ':break;

            default:

                while(ch>='0'&&ch<='9')

                { /*判定为数字*/

                    ex[t]=ch;t++;

                    ch=str[i];i++;

                }

                i--;

                ex[t]=' ';t++;

        }

        ch=str[i];i++;

    }

    while(top!=0)

    {

        ex[t]=stack[top];

        t++;top--;

    }

    ex[t]=' ';

    printf("\n\t原来表达式：");

    for(j=1;j<sum;j++)

        printf("%c",str[j]);

    printf("\n\t逆波兰式：",ex);

    for(j=1;j<t;j++)

        printf("%c",ex[j]);

}

 

void compvalue()

{ /*计算后缀表达式的值*/

    float stack[max],d; /*作为栈使用*/

    char ch;

    int t=1,top=0; /*t为ex下标，top为stack下标*/

    ch=ex[t];t++;

    while(ch!=' ')

    {

        switch(ch)

        {

            case '+':

                stack[top-1]=stack[top-1]+stack[top];

                top--;

                break;

            case '-':

                stack[top-1]=stack[top-1]-stack[top];

                top--;

                break;

            case '*':

                stack[top-1]=stack[top-1]*stack[top];

                top--;

                break;

            case '/':

                if(stack[top]!=0) stack[top-1]=stack[top-1]/stack[top];

                else

                {

                    printf("\n\t除零错误!\n");

                    exit(0); /*异常退出*/

                }

                top--;

                break;

            default:

                d=0;

                while(ch>='0'&&ch<='9')

                {

                    d=10*d+ch-'0'; /*将数字字符转化为对应的数值*/

                    ch=ex[t];t++;

                }

                top++;

                stack[top]=d;

        }

        ch=ex[t];

        t++;

    }

    printf("\n\t计算结果:%g\n",stack[top]);

}

 

int main()

{

    trans();

    compvalue();

    system("pause");

    return 0;

}