Expression Evaluation（表达式求值）

20080927
数据结构中栈的应用。

#include<ctype.h>

#include<stdio.h>

#include<stdlib.h>

#include<bios.h>

typedef struct stack

{

    union

    {

        float value;

        char sign;

    }data;

    struct stack *down;

}ST;

void finish(ST *topv);

void c2(ST **ptopv,ST **ptops);

void error();

ST *compute(ST *a,char sign,ST *b);

void push(ST **ptop,ST *in);

ST *pop(ST **ptop);

char *read(ST *r,char *class,char *ch);

char convert(char sign);

void rsgs(char *p,char max);

int rsgc();

void option(ST **ptopv,ST **ptops,ST *cu,char *pclass);

void main()

{

    ST *topv=0,*tops=0,*cu;

    char ch[71],class,*p=ch;

    printf("\n Expression Evaluation V20080928 by roundsheep");

    printf("\n\n Max String:70");

    printf("\n\n Max Significant Digits:6");

    printf("\n\n Max Decimal Digits:5");

    printf("\n\n Can only use the digit or +-*/()");

    printf("\n\n Please input expression:\n\n ");

    rsgs(ch,70);

    while(1)

    {

        cu=(ST *)malloc(sizeof(ST));

        p=read(cu,&class,p);

        if(p==0||cu==0)error();

        option(&topv,&tops,cu,&class);

        if(*p==0)

        {

            while(tops!=0)c2(&topv,&tops);

            if(tops==0&&topv->down==0)finish(topv);

            else error();

        }

    }

}

ST *compute(ST *a,char sign,ST *b)

{

    switch(sign)

    {

        case '+':a->data.value+=b->data.value;break;

        case '-':a->data.value-=b->data.value;break;

        case '*':a->data.value*=b->data.value;break;

        case '/':a->data.value/=b->data.value;

    }

    return a;

}

void push(ST **ptop,ST *in)

{

    in->down=*ptop;

    *ptop=in;

}

ST *pop(ST **ptop)

{

    ST *t;

    if(*ptop==0)return 0;

    t=*ptop;

    *ptop=(*ptop)->down;

    return t;

}

char *read(ST *r,char *pclass,char *ch)

{

    float b;

    switch(*ch)

    {

        case '+':

        case '-':

        case '*':

        case '/':

        case '(':

        case ')':

            r->data.sign=*ch;

            *pclass='s';

            return ch+1;

    }

    if(!isdigit(*ch))return 0;

    *pclass='v';

    for(r->data.value=0;isdigit(*ch);ch++)

    {

        r->data.value*=10;

        r->data.value+=*ch-48;

    }

    if(*ch!='.')return ch;

    ch++;

    if(!isdigit(*ch))return 0;

    for(b=10;isdigit(*ch)&&b<10e6;ch++,b*=10)

    r->data.value+=(*ch-48)/b;

    return ch;

}

char convert(char sign)

{

    char c;

    switch(sign)

    {

        case '+':c=0;break;

        case '-':c=1;break;

        case '*':c=2;break;

        case '/':c=3;break;

        case '(':c=4;break;

        case ')':c=5;

    }

    return c;

}

void error()

{

    printf("\n\n Error!");

    rsgc();

    exit(0);

}

void c2(ST **ptopv,ST **ptops)

{

    ST *com1,*com2;

    com2=pop(ptopv);

    com1=pop(ptopv);

    if(com1==0)error();

    com1=compute(com1,pop(ptops)->data.sign,com2);

    push(ptopv,com1);

}

void finish(ST *topv)

{

    printf("\n\n Result:\n\n %.3f",topv->data.value);

    rsgc();

    exit(0);

}

int rsgc()

{

    int c=0,key;

    key=bioskey(0);

    switch(key)

    {

        case 11779:c=6;exit(0);/* quit */

        case 3592:c=5;break;/* backspace */

        case 7181:c=10;break;/* enter */

        case 18432:c=1;break;/* up down left right */

        case 20480:c=2;break;

        case 19200:c=3;break;

        case 19712:c=4;break;

    }

    if(c)return c;

    return key&0xff;

}

void rsgs(char *p,char max)

{

    char s=max;

    do

    {

        do

        {

        *p=rsgc();

      }while(*p==5&&s==max||*p!=10&&*p!=5&&s==0);

      if(*p==5)

      {

        printf("\b \b");

        s+=2;

        p-=2;

      }

        else if(*p==10){*p=0;return;}

        else if(*p>=33&&*p<=126)putchar(*p);

        else putchar(' ');

        p++;

    }while(s--);

    *--p=0;

}

void option(ST **ptopv,ST **ptops,ST *cu,char *pclass)

{

    char t,cp[6][6]=

    {

        {1,1,-1,-1,-1,1},

        {1,1,-1,-1,-1,1},

        {1,1,1,1,-1,1},

        {1,1,1,1,-1,1},

        {-1,-1,-1,-1,-1,0},

        {-1,-1,-1,-1,-2,1}

    };

    if(*pclass=='v'){push(ptopv,cu);return;}

    if(*ptops==0){push(ptops,cu);return;}

    t=cp[convert((*ptops)->data.sign)][convert(cu->data.sign)];

    switch(t)

    {

        case -2:error();

        case 0:pop(ptops);break;

        case -1:push(ptops,cu);break;

        case 1:{c2(ptopv,ptops);option(ptopv,ptops,cu,pclass);}

    }

}