1 /*
2  * Exercise 4-5. Add access to library functions like sin, exp, and pow. See
3  * <math.h> in Appendix B, Section 4.
4  */
5 
6 #include <stdio.h>
7 #include <stdlib.h> /* for atof() */
8 #include <math.h>
9 #include <string.h>
10 
11 #define MAXOP 100 /* max size of operand or operator */
12 #define NUMBER '0' /* signal that a number was found */
13 #define IDENTIFIER '1' /* signal that an identifier was found */
14 
15 int getop(char []);
16 void push(double);
17 double pop(void);
18 double printtop(void);
19 int duplicate(void);
20 int swap(void);
21 void clear(void);
22 
23 /* reverse Polish calculator */
24 int main() {
25 	int type;
26 	double op2;
27 	char s[MAXOP];
28 	while ((type = getop(s)) != EOF) {
29 		switch (type) {
30 		case NUMBER:
31 			push(atof(s));
32 			break;
33 		case IDENTIFIER:
34 			if (strcmp(s, "sin") == 0)
35 				push(sin(pop()));
36 			else if (strcmp(s, "cos") == 0)
37 				push(cos(pop()));
38 			else if (strcmp(s, "exp") == 0)
39 				push(exp(pop()));
40 			break;
41 		case '+':
42 			push(pop() + pop());
43 			break;
44 		case '*':
45 			push(pop() * pop());
46 			break;
47 		case '-':
48 			op2 = pop();
49 			push(pop() - op2);
50 			break;
51 		case '/':
52 			op2 = pop();
53 			if (op2 != 0.0)
54 				push(pop() / op2);
55 			else
56 				printf("error: zero divisor\n");
57 			break;
58 		case '%':
59 			op2 = pop();
60 			if (op2 != 0.0)
61 				push((int) pop() % (int) op2);
62 			else
63 				printf("error: zero divisor\n");
64 			break;
65 		case '?':
66 			printf("\t%.8g\n", printtop());
67 			break;
68 		case '#':
69 			if (duplicate() == 0)
70 				printf("error: can't duplicate\n");
71 			break;
72 		case '~':
73 			if (swap() == 0)
74 				printf("error: swap failed, stack needs two numbers\n");
75 			break;
76 		case '!':
77 			clear();
78 			break;
79 		case '\n':
80 			printf("\t%.8g\n", pop());
81 			break;
82 		default:
83 			printf("error: unknown command %s\n", s);
84 			break;
85 		}
86 	}
87 }
88 
89 #define MAXVAL 100 /* maximum depth of val stack */
90 
91 int sp = 0; /* next free stack position */
92 double val[MAXVAL]; /* value stack */
93 
94 /* push: push f onto value stack */
95 void push (double f) {
96 	if (sp < MAXVAL)
97 		val[sp++] = f;
98 	else
99 		printf ("error: stack full, can't push %g\n", f);
100 }
101 
102 /* pop: pop and return top value from stack */
103 double pop(void) {
104 	if (sp > 0)
105 		return val[--sp];
106 	else {
107 		printf("error: stack empty\n");
108 		return 0.0;
109 	}
110 }
111 
112 /* printtop: print the top value of the stack without popping it */
113 double printtop(void) {
114 	if (sp > 0)
115 		return val[sp-1];
116 	else {
117 		printf("error: stack empty\n");
118 		return 0.0;
119 	}
120 }
121 
122 /* duplicate: duplicate the top value of the stack
123  * return 1 if successful, 0 on failure */
124 int duplicate(void) {
125 	if (sp <= 0) {
126 		return 0;
127 	} else if (sp >= MAXVAL) {
128 		return 0;
129 	} else {
130 		val[sp] = val[sp-1];
131 		sp++;
132 		return 1;
133 	}
134 }
135 
136 /* swap: swap the top two values of the stack
137  * return 1 if successful, 0 on failure */
138 int swap(void) {
139 	if (sp > 1) {
140 		int temp = val[sp-1];
141 		val[sp-1] = val[sp-2];
142 		val[sp-2] = temp;
143 		return 1;
144 	}
145 	return 0;
146 }
147 
148 /* clear: clear the stack */
149 void clear(void) {
150 	sp = 0;
151 }
152 
153 #include <ctype.h>
154 
155 int getch(void);
156 void ungetch(int);
157 
158 /* getop: get next operator or numeric operand */
159 int getop(char s[]) {
160 	int i, c;
161 	while ((s[0] = c = getch()) == ' ' || c == '\t')
162 		;
163 	s[1] = '\0';
164 	i = 0;
165 	if (isalpha(c)) {
166 		while (isalpha(s[++i] = c = getch()))
167 			;
168 		s[i] = '\0';
169 		if (c != EOF)
170 			ungetch(c);
171 		return IDENTIFIER;
172 	}
173 	/* negative number or minus */
174 	if (c == '-') {
175 		s[++i] = c = getch();
176 		if (!isdigit(c) && c != '.') {
177 			ungetch(c);
178 			return '-';
179 		}
180 	}
181 	if (!isdigit(c) && c != '.')
182 		return c; /* not a number */
183 	if (isdigit(c)) /* collect integer part */
184 		while (isdigit(s[++i] = c = getch()))
185 			;
186 	if (c == '.') /* collect fraction part */
187 		while (isdigit(s[++i] = c = getch()))
188 			;
189 	s[i] = '\0';
190 	if (c != EOF)
191 		ungetch(c);
192 	return NUMBER;
193 }
194 
195 #define BUFSIZE 100
196 
197 char buf[BUFSIZE]; /* buffer for ungetch */
198 int bufp = 0;
199 
200 /* get a (possibly pushed back) character */
201 int getch(void) {
202 	return (bufp > 0) ? buf[--bufp] : getchar();
203 }
204 
205 /* push character back on input */
206 void ungetch(int c) {
207 	if (bufp >= BUFSIZE)
208 		printf("ungetch: too many characters\n");
209 	else
210 		buf[bufp++] = c;
211 }
212 
213 /*
214 void printstack(void);
215 		printstack();
216 void printstack(void) {
217 	for (int i = 0; i < sp; i++)
218 		printf("%g ", val[i]);
219 	printf("\n");
220 }
221 */