C 프로그래밍 언어 학습 노트(二)

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

#define MAXOP 100
#define NUMBER '0'
#define BUFSIZE 100
#define MAXVAL 100
int sp = 0;
double val[MAXVAL];
char buf[BUFSIZE];
int bufp = 0;

int getop(char s[]);
void push(double x);
double pop(void);
int getch(void);
void ungetch(int);

int main()
{
    int type;
    double op2,op1;
    char s[MAXOP];

    while((type = getop(s)) != EOF)
    {
        switch(type)
        {
            case NUMBER:
                push(atof(s));
                break;
            case '+':
                push(pop() + pop());
                break;
            case '-':
                op2 = pop();
                push(pop() - op2);
                break;
            case '*':
                push(pop() * pop());
                break;
            case '/':
                op2 = pop();
                if(op2 != 0.0)
                    push(pop() / op2);
                else
                  printf("error:zero divisor
");
                break;
            case '%':
                op2 = pop();
                push((int)pop() % (int)op2);
                break;
            case '
':
                printf("\t%.8g
", pop());
                break;
            default:
                printf("error:unknown command %s
", s);
                break;

        }
    }
    return 0;
}

void push(double f)
{
    /*printf("f = %lf
", f);*/
    if(sp < MAXVAL)
      val[sp++] = f;
    else
      printf("error:the stack is full
");
}

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

int getop(char s[])
{
    int c, i;

    while((s[0] = c = getch()) == ' ' || c == '\t')
      ;
    s[1] = '\0';
    if(!isdigit(c) && c != '.')
    {
        int c2;
        /*           ，       */
         /*    printf("c = %c
",c);*/
        if( c == '
' || !(c == '-' || c == '+'))
        {
            return c;
        }
        /*       ，       ，         */
        c2 = getch();
        ungetch(c2);
        /*printf("c2 = %c
", c2);*/
        if(!isdigit(c2))
        {
            return c;
        }
    }

    i = 0;

    if(isdigit(c) || c == '-')
    {
        while((s[++i] = c = getch()) && isdigit(c))
          ;
    }
    if(c == '.')
    {
        while((s[++i] = c = getch()) && isdigit(c))
          ;
    }
    s[i] = '\0';
    /*printf("s = %s
", s);*/
    if(c != EOF)
    {
        ungetch(c);
    }
    return NUMBER;
}

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

void ungetch(int c)
{
    if(bufp < BUFSIZE)
    {
        buf[bufp++] = c;
    }
    else
    {
        printf("error:the buf is full
");
    }
}