[C] - 逆波兰计算器

来源：网络

 

  
    

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

   
     #define
   
      MAXOP 100
   
     

   
     #define
   
      NUMBER '0'
   
     


   
     int
   
      getop(
   
     char
   
      []);

   
     void
   
      push(
   
     double
   
     );

   
     double
   
      pop(
   
     void
   
     );


   
     int
   
      getch(
   
     void
   
     );

   
     void
   
      ungetch(
   
     int
   
     );


   
     int
   
      getop(
   
     char
   
      s[])
{
 
   
     int
   
      i,c;
 
   
     while
   
      ((s[
   
     0
   
     ]
   
     =
   
     c
   
     =
   
     getch())
   
     ==
   
     '
   
      
   
     '
   
     ||
   
      c
   
     ==
   
     '
   
     \t
   
     '
   
     );
 s[
   
     1
   
     ]
   
     =
   
     '
   
     \0
   
     '
   
     ;
 
   
     if
   
     (
   
     !
   
     isdigit(c)
   
     &&
   
     c
   
     !=
   
     '
   
     .
   
     '
   
     )
 
   
     return
   
      c;
 i
   
     =
   
     0
   
     ;
 
   
     if
   
     (isdigit(c))
 
   
     while
   
      (isdigit(s[
   
     ++
   
     i]
   
     =
   
     c
   
     =
   
     getch()));
 
   
     if
   
      (c
   
     ==
   
     '
   
     .
   
     '
   
     )
 
   
     while
   
      (isdigit(s[
   
     ++
   
     i]
   
     =
   
     c
   
     =
   
     getch()));
 s[i]
   
     =
   
     '
   
     \0
   
     '
   
     ;
 
   
     if
   
      (c
   
     !=
   
     EOF)
 ungetch(c);
 
   
     return
   
      NUMBER;
}




   
     #define
   
      BUFSIZE 100
   
     

   
     char
   
      buf[BUFSIZE];

   
     int
   
      bufp
   
     =
   
     0
   
     ;


   
     int
   
      getch(
   
     void
   
     )
{
 
   
     return
   
     (bufp
   
     >
   
     0
   
     ) 
   
     ?
   
      buf[
   
     --
   
     bufp]:getchar();
}

   
     void
   
      ungetch(
   
     int
   
      c)
{
 
   
     if
   
      (bufp
   
     >=
   
     BUFSIZE)
 printf(
   
     "
   
     ungetch:too many characters\n
   
     "
   
     );
 
   
     else
   
     
 buf[bufp
   
     ++
   
     ]
   
     =
   
     c;
}
main()
{
 
   
     int
   
      type;
 
   
     double
   
      op2;
 
   
     char
   
      s[MAXOP];
 
   
     while
   
      ((type
   
     =
   
     getop(s))
   
     !=
   
     EOF) {
 
   
     switch
   
      (type) {
 
   
     case
   
      NUMBER:
 push(atof(s));
 
   
     break
   
     ;

 
   
     case
   
      
   
     '
   
     +
   
     '
   
     :
 push(pop()
   
     +
   
     pop());
 
   
     break
   
     ;
 
   
     case
   
      
   
     '
   
     *
   
     '
   
     :
 push(pop()
   
     *
   
     pop());
 
   
     break
   
     ;
 
   
     case
   
      
   
     '
   
     -
   
     '
   
     :
 op2
   
     =
   
     pop();
 push(pop()
   
     -
   
     op2);
 
   
     break
   
     ;
 
   
     case
   
      
   
     '
   
     /
   
     '
   
     :
 op2
   
     =
   
     pop();
 
   
     if
   
      (op2
   
     !=
   
     0.0
   
     )
 push(pop()
   
     /
   
     op2);
 
   
     else
   
     
 printf(
   
     "
   
     error:zero divisor\n
   
     "
   
     );
 
   
     break
   
     ;
 
   
     /*
   
     case '/n':
 printf("\t%.8g\n",pop());
 break;
   
     */
   
     
 
   
     case
   
      
   
     0x0a
   
     :
 printf(
   
     "
   
     \t%.8g\n
   
     "
   
     ,pop());
 
   
     break
   
     ;

 
   
     default
   
     :
 printf(
   
     "
   
     error:unknown command %s\n
   
     "
   
     ,s);
 
   
     break
   
     ;
 }
 }
 
   
     return
   
      
   
     0
   
     ;
}



   
     #define
   
      MAXVAL 100
   
     


   
     int
   
      sp
   
     =
   
     0
   
     ;

   
     double
   
      val[MAXVAL];


   
     void
   
      push(
   
     double
   
      f)
{
 
   
     if
   
      (sp
   
     <
   
     MAXVAL)
 val[sp
   
     ++
   
     ]
   
     =
   
     f;
 
   
     else
   
     
 printf(
   
     "
   
     error:strack full,can't push %g\n
   
     "
   
     ,f);
}

   
     double
   
      pop(
   
     void
   
     )
{
 
   
     if
   
      (sp
   
     >
   
     0
   
     )
 
   
     return
   
      val[
   
     --
   
     sp];
 
   
     else
   
      {
 printf(
   
     "
   
     error:stack empty\n
   
     "
   
     );
 
   
     return
   
      
   
     0.0
   
     ;
 }
}