calc_adv.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <ctype.h>
   4
   5 #define MAXOP 100
   6 #define NUMBER '0'
   7 #define MAXVAL 100
   8 #define BUFSIZE 100
   9
  10 int getop(char[]);
  11 void push(double);
  12 double pop(void);
  13
  14 int main()
  15 {
  16         int type;
  17         double op2;
  18         char s[MAXOP];
  19
  20         while((type = getop(s)) != EOF)
  21         {
  22                 switch(type)
  23                 {
  24                         case NUMBER:
  25                                 push(atof(s));
  26                                 break;
  27                         case '+':
  28                                 push(pop() + pop());
  29                                 break;
  30                         case '*':
  31                                 push(pop() * pop());
  32                                 break;
  33                         case '-':
  34                                 op2 = pop();
  35                                 push(pop() - op2);
  36                                 break;
  37                         case '/':
  38                                 op2 = pop();
  39                                 if(op2 != 0.0)
  40                                         push(pop() / op2);
  41                                 else
  42                                         printf("error: zero divisor\n");
  43                                 break;
  44                         case '%':
  45                                 op2 = pop();
  46                                 if(op2 != 0.0)
  47                                 {
  48                                         push((int)(pop()) % (int)(op2));
  49                                 } else {
  50                                         printf("error: zero divisor\n");
  51                                 }
  52                                 break;
  53                         case '\n':
  54                                 printf("\t%.8g\n", pop());
  55                                 break;
  56                         default:
  57                                 printf("error: unknown command %s\n", s);
  58                                 break;
  59                 }
  60         }
  61         return 0;
  62 }
  63
  64 int sp = 0;
  65 double val[MAXVAL];
  66
  67 /* push f onto value stack */
  68 void push(double f)
  69 {
  70         if(sp < MAXVAL)
  71                 val[sp++] = f;
  72         else
  73                 printf("error: stack full\n");
  74 }
  75
  76
  77 /* pop and return top value from stack */
  78 double pop(void)
  79 {
  80         if(sp > 0)
  81                 return val[--sp];
  82         else
  83         {
  84                 printf("error: stack empty\n");
  85                 return 0.0;
  86         }
  87 }
  88
  89 int getch(void);
  90 void ungetch(int);
  91
  92 /* get next operator or numberic operand */
  93 int getop(char s[])
  94 {
  95         int i, c;
  96
  97         while ((s[0] = c = getch()) == ' ' || c == '\t')
  98                 ;
  99         s[1] = '\0';
 100         if(!isdigit(c) && c != '.')
 101                 return c;
 102         i = 0;
 103         if(isdigit(c))
 104                 while(isdigit(s[++i] = c = getch()))
 105                         ;
 106         if(c == '.')
 107                 while(isdigit(s[++i] = c = getch()))
 108                         ;
 109         s[i] = '\0';
 110         if(c != EOF)
 111                 ungetch(c);
 112         return NUMBER;
 113 }
 114
 115 char buf[BUFSIZE];
 116 int bufp = 0;
 117
 118 int getch(void)
 119 {
 120         return (bufp > 0) ? buf[--bufp] : getchar();
 121 }
 122
 123 void ungetch(int c)
 124 {
 125         if(bufp >= BUFSIZE)
 126                 printf("ungetch: too many characters\n");
 127         else
 128                 buf[bufp++] = c;
 129 }