逆波兰计算器.c

经典数据结构编程

#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;
}
}