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
|
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#define NUMBER '0'
#define MAXLINE 1000
#define MAXVAL 100
int getop(char[]);
void push(double);
double pop(void);
void clear(void);
double peek(void);
// Naïve implementation of remainder operation
double frem(double f1, double f2) {
return f1 - (f2 * (int)(f1 / f2));
}
/**
* Reverse polish notation calculator
*/
int main(void) {
double op2;
char* line = NULL;
size_t line_len = 0;
while (getline(&line, &line_len, stdin) != -1) {
char* tok = strtok(line, " ");
do {
int type = getop(tok);
switch (type) {
case NUMBER:
push(atof(tok));
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 division attempted!\n");
break;
case '%':
op2 = pop();
if (op2 != 0.0)
push(frem(pop(), op2));
else
printf("error: zero division attempted!\n");
break;
case '~':
clear();
break;
default:
//printf("unknown command %s\n", tok); // Just ignore it?
break;
}
} while ((tok = strtok(NULL, " ")) != NULL);
printf("\t%.8g\n", pop());
}
free(line); // or, don't bother since we exit the program next...
return 0;
}
int sp; // Stack position
double val[MAXVAL]; // Value stack
void push(double f) {
if (sp < MAXVAL) {
val[sp++] = f;
} else {
printf("error, stack full\n");
}
}
double pop(void) {
if (sp >= 0) {
return val[--sp];
} else {
printf("error, empty stack\n");
return 0.0;
}
}
double peek(void) {
if (sp >= 0) {
return val[sp-1];
} else {
printf("error, empty stack\n");
return 0.0;
}
}
void clear(void) {
sp = 0;
}
int getop(char s[]) {
char c = s[0];
if (!isdigit(c) && c != '.')
return c;
return NUMBER;
}
|
