求一个用C语言开发一个多功能简易计算器，基本信息包括:四则运算、常见单位转换。使之能提供以下两大部分功能

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define DATA                0
#define PARENTHESIS_LEFT    1
#define ADD_SUB                2
#define MUL_DIV                3
#define PARENTHESIS_RIGHT    4
#define MAX_LEN        256

union Value
{
    double value_f;
    char value_c;
};

struct SIGN
{
    union Value value;
    unsigned int flag;    //0.数据。1.2.3.符号
};

int main()
{
    double value[20];
    char buf[MAX_LEN],buf_temp[20];
    int i=0,mm=0,count=0,sign_len=-1,lose_len=0;;
    struct SIGN m_sign[20],m_infix[50],m_posfix[50];
    printf("请输入表达式，以#结束:");
    if(fgets(buf,MAX_LEN,stdin)!=NULL)
    {
        while(i<MAX_LEN&&buf[i]!='#')
        {
            while((buf[i]>='0'&&buf[i]<='9')||buf[i]=='.')    //读取数据
            {
                buf_temp[mm++]=buf[i];
                if(mm>=10)
                {
                    printf("出错！\n");
                    return -1;
                }
                i++;
            }
            if(mm>0)                                        //数据入栈
            {
                buf_temp[mm]='\0';
                m_infix[count].flag=DATA;
                m_infix[count].value.value_f=atof(buf_temp);
                count++;
                mm=0;
                continue;
            }

            switch(buf[i])
            {
            case '+':
                m_infix[count].flag=ADD_SUB;
                m_infix[count].value.value_c='+';
                count++;
                    break;
            case '-':
                m_infix[count].flag=ADD_SUB;
                m_infix[count].value.value_c='-';
                count++;
                break;
            case '*':
                m_infix[count].flag=MUL_DIV;
                m_infix[count].value.value_c='*';
                count++;
                break;
            case '/':
                m_infix[count].flag=MUL_DIV;
                m_infix[count].value.value_c='/';
                count++;
                break;
            case '(':
                m_infix[count].flag=PARENTHESIS_LEFT;
                m_infix[count].value.value_c='(';
                count++;
                break;
            case ')':
                m_infix[count].flag=PARENTHESIS_RIGHT;
                m_infix[count].value.value_c=')';
                count++;
                break;
            default:break;
            }
            i++;
        }

        mm=0;
        for(i=0;i<count;i++)
        {
            if(m_infix[i].flag==DATA)
            {
                m_posfix[mm].flag=m_infix[i].flag;
                m_posfix[mm].value.value_f=m_infix[i].value.value_f;
                mm++;
            }
            else
            {
                if(sign_len<0||m_infix[i].flag==PARENTHESIS_LEFT)
                {
                    lose_len++;
                    sign_len++;
                    m_sign[sign_len].flag=m_infix[i].flag;
                    m_sign[sign_len].value.value_c=m_infix[i].value.value_c;
                }
                else if(m_infix[i].flag==PARENTHESIS_RIGHT)
                {
                    lose_len++;
                    while(m_sign[sign_len].flag != PARENTHESIS_LEFT)
                    {
                        m_posfix[mm].flag=m_sign[sign_len].flag;
                        m_posfix[mm].value.value_c=m_sign[sign_len].value.value_c;
                        sign_len--;
                        mm++;
                        if(sign_len<0)
                        {
                            printf("出错！\n");
                            break;
                        }
                    }
                    sign_len--;
                }
                else if(m_infix[i].flag<m_sign[sign_len].flag)
                {
                    while(m_infix[i].flag<=m_sign[sign_len].flag&&m_sign[sign_len].flag!=PARENTHESIS_LEFT)
                    {
                        m_posfix[mm].flag=m_sign[sign_len].flag;
                        m_posfix[mm].value.value_c=m_sign[sign_len].value.value_c;
                        sign_len--;
                        mm++;
                        if(sign_len<0)
                            break;
                    }
                    sign_len++;
                    m_sign[sign_len].flag=m_infix[i].flag;
                    m_sign[sign_len].value.value_c=m_infix[i].value.value_c;
                }
                else
                {
                    sign_len++;
                    m_sign[sign_len].flag=m_infix[i].flag;
                    m_sign[sign_len].value.value_c=m_infix[i].value.value_c;
                    printf("in2--%d,%d,%c\n",i,m_sign[sign_len].flag,m_sign[sign_len].value.value_c);
                }
            }
        }
        while(sign_len>=0)
        {
            m_posfix[mm].flag=m_sign[sign_len].flag;
            m_posfix[mm].value.value_c=m_sign[sign_len].value.value_c;
            sign_len--;
            mm++;
        }

        for(i=0;i<mm;i++)
        {
            if(m_posfix[i].flag==DATA)
                printf("%g,",m_posfix[i].value.value_f);
            else
                printf("%c,",m_posfix[i].value.value_c);
        }
        printf("\n");

        count=0;
        for(i=0;i<mm;i++)
        {
            if(m_posfix[i].flag==DATA)
                value[++count]=m_posfix[i].value.value_f;
            else
            {
                switch(m_posfix[i].value.value_c)
                {
                case '+':value[count-1]=value[count-1]+value[count];break;
                case '-':value[count-1]=value[count-1]-value[count];break;
                case '*':value[count-1]=value[count-1]*value[count];break;
                case '/':value[count-1]=value[count-1]/value[count];break;
                }
                count--;
            }
        }
        printf("result=%g\n",value[1]);
    }
    else
    {
        printf("输入的表达式有误，请重新输入!\n");
    }

    return 0;
}