blob: 83a45a9946cccc99796e55bf85f8e3dc93655941 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
|
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#define MAXOP 100 /* max size of operand or operator */
#define NUMBER '0' /* signal that a number was found */
#define MAXVAL 100 /* max depth of val stack */
#define BUFSIZE 100
int sp = 0; /* next free stack position */
double val[MAXVAL]; /* value stack */
int bufp = 0; /* next free position in buf */
char buf[BUFSIZE]; /* buffer for ungetch */
/* get next operator or numeric operand */
int getop(char[]);
/* push f onto value stack */
void push(double);
/* pop and return top value from stack */
double pop();
/* reverse Polish calculator */
int main(int argc, char *argv[]) {
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: division by zero\n");
break;
case '%':
op2 = pop();
if (op2 != 0.0)
push((int)pop() % (int)op2);
else
printf("error: division by zero\n");
break;
case '\n':
printf("\t%.8g\n", pop());
break;
default:
printf("error: unknown command %s\n", s);
}
}
return 0;
}
void push(double f) {
if (sp < MAXVAL)
val[sp++] = f;
else
printf("error: stack empty\n");
}
double pop() {
if (sp > 0)
return val[--sp];
else {
printf("error: stack empty\n");
return 0.0;
}
}
int getch() { return (bufp > 0) ? buf[--bufp] : getchar(); }
void ungetch(int c) {
if (bufp >= BUFSIZE)
printf("ungetch: too many characters\n");
else
buf[bufp++] = c;
}
int getop(char s[]) {
int i, c;
while ((s[0] = c = getch()) == ' ' || c == '\t')
;
s[1] = 0;
if (!isdigit(c) && c != '.' && c != '-')
return c;
i = 0;
if (isdigit(c))
while (isdigit(s[++i] = c = getch()))
;
if (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;
}
|
