calc.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 '\n':
  45                                 printf("\t%.8g\n", pop());
  46                                 break;
  47                         default:
  48                                 printf("error: unknown command %s\n", s);
  49                                 break;
  50                 }
  51         }
  52         return 0;
  53 }
  54
  55
  56
  57
  58 int sp = 0;
  59 double val[MAXVAL];
  60
  61
  62 /* push f onto value stack */
  63 void push(double f)
  64 {
  65         if(sp < MAXVAL)
  66                 val[sp++] = f;
  67         else
  68                 printf("error: stack full\n");
  69 }
  70
  71
  72 /* pop and return top value from stack */
  73 double pop(void)
  74 {
  75         if(sp > 0)
  76                 return val[--sp];
  77         else
  78         {
  79                 printf("error: stack empty\n");
  80                 return 0.0;
  81         }
  82 }
  83
  84
  85
  86 int getch(void);
  87 void ungetch(int);
  88
  89 /* get next operator or numberic operand */
  90 int getop(char s[])
  91 {
  92         int i, c;
  93
  94         while ((s[0] = c = getch()) == ' ' || c == '\t')
  95                 ;
  96         s[1] = '\0';
  97         if(!isdigit(c) && c != '.')
  98                 return c;
  99         i = 0;
 100         if(isdigit(c))
 101                 while(isdigit(s[++i] = c = getch()))
 102                         ;
 103         if(c == '.')
 104                 while(isdigit(s[++i] = c = getch()))
 105                         ;
 106         s[i] = '\0';
 107         if(c != EOF)
 108                 ungetch(c);
 109         return NUMBER;
 110 }
 111
 112 char buf[BUFSIZE];
 113 int bufp = 0;
 114
 115 int getch(void)
 116 {
 117         return (bufp > 0) ? buf[--bufp] : getchar();
 118 }
 119
 120
 121 void ungetch(int c)
 122 {
 123         if(bufp >= BUFSIZE)
 124                 printf("ungetch: toomany characters\n");
 125         else
 126                 buf[bufp++] = c;
 127 }