1 5dc21454 2023-07-14 jrmu /*
  2 5dc21454 2023-07-14 jrmu  * Exercise 4-11. Modify getop so that it doesn't need to use ungetch. Hint:
  3 5dc21454 2023-07-14 jrmu  * use an internal static variable.
  4 5dc21454 2023-07-14 jrmu  */
  5 5dc21454 2023-07-14 jrmu 
  6 5dc21454 2023-07-14 jrmu #include <stdio.h>
  7 5dc21454 2023-07-14 jrmu #include <stdlib.h> /* for atof() */
  8 5dc21454 2023-07-14 jrmu #include <math.h> /* for math functions */
  9 5dc21454 2023-07-14 jrmu #include <string.h> /* for strcmp() */
 10 5dc21454 2023-07-14 jrmu #include <ctype.h> /* for tolower() */
 11 5dc21454 2023-07-14 jrmu 
 12 5dc21454 2023-07-14 jrmu #define MAXOP 100 /* max size of operand or operator */
 13 5dc21454 2023-07-14 jrmu #define NUMBER '0' /* signal that a number was found */
 14 5dc21454 2023-07-14 jrmu #define IDENTIFIER '1' /* signal that an identifier was found */
 15 5dc21454 2023-07-14 jrmu #define VARIABLE '2' /* signal that a variable was found */
 16 5dc21454 2023-07-14 jrmu #define ASSIGNMENT '3' /* signal that a variable was found */
 17 5dc21454 2023-07-14 jrmu #define LETTERS 26 /* number of letters in alphabet */
 18 5dc21454 2023-07-14 jrmu 
 19 5dc21454 2023-07-14 jrmu int getop(char []);
 20 5dc21454 2023-07-14 jrmu void push(double);
 21 5dc21454 2023-07-14 jrmu double pop(void);
 22 5dc21454 2023-07-14 jrmu double printtop(void);
 23 5dc21454 2023-07-14 jrmu int duplicate(void);
 24 5dc21454 2023-07-14 jrmu int swap(void);
 25 5dc21454 2023-07-14 jrmu void clear(void);
 26 5dc21454 2023-07-14 jrmu int assign(int, double);
 27 5dc21454 2023-07-14 jrmu double eval(int index);
 28 5dc21454 2023-07-14 jrmu 
 29 5dc21454 2023-07-14 jrmu /* reverse Polish calculator */
 30 5dc21454 2023-07-14 jrmu int main() {
 31 5dc21454 2023-07-14 jrmu 	int type;
 32 5dc21454 2023-07-14 jrmu 	double op2, val;
 33 5dc21454 2023-07-14 jrmu 	char s[MAXOP];
 34 5dc21454 2023-07-14 jrmu 	int index;
 35 5dc21454 2023-07-14 jrmu 	while ((type = getop(s)) != EOF) {
 36 5dc21454 2023-07-14 jrmu 		switch (type) {
 37 5dc21454 2023-07-14 jrmu 		case NUMBER:
 38 5dc21454 2023-07-14 jrmu 			push(atof(s));
 39 5dc21454 2023-07-14 jrmu 			break;
 40 5dc21454 2023-07-14 jrmu 		case IDENTIFIER:
 41 5dc21454 2023-07-14 jrmu 			if (strcmp(s, "sin") == 0)
 42 5dc21454 2023-07-14 jrmu 				push(sin(pop()));
 43 5dc21454 2023-07-14 jrmu 			else if (strcmp(s, "cos") == 0)
 44 5dc21454 2023-07-14 jrmu 				push(cos(pop()));
 45 5dc21454 2023-07-14 jrmu 			else if (strcmp(s, "exp") == 0)
 46 5dc21454 2023-07-14 jrmu 				push(exp(pop()));
 47 5dc21454 2023-07-14 jrmu 			break;
 48 5dc21454 2023-07-14 jrmu 		case VARIABLE:
 49 5dc21454 2023-07-14 jrmu 			index = tolower(s[0]) - 'a';
 50 5dc21454 2023-07-14 jrmu 			if (0 <= index && index < LETTERS) {
 51 5dc21454 2023-07-14 jrmu 				push(eval(index));
 52 5dc21454 2023-07-14 jrmu 			} else {
 53 5dc21454 2023-07-14 jrmu 				printf("error: variable must be single letter\n");
 54 5dc21454 2023-07-14 jrmu 			}
 55 5dc21454 2023-07-14 jrmu 			break;
 56 5dc21454 2023-07-14 jrmu 		case ASSIGNMENT:
 57 5dc21454 2023-07-14 jrmu 			index = tolower(s[0]) - 'a';
 58 5dc21454 2023-07-14 jrmu 		        val = atof(s+2);
 59 5dc21454 2023-07-14 jrmu 			if (!assign(index, val)) {
 60 5dc21454 2023-07-14 jrmu 				printf("error: assignment failed, variable needs to be single letter\n");
 61 5dc21454 2023-07-14 jrmu 			}
 62 5dc21454 2023-07-14 jrmu 			break;
 63 5dc21454 2023-07-14 jrmu 		case '+':
 64 5dc21454 2023-07-14 jrmu 			push(pop() + pop());
 65 5dc21454 2023-07-14 jrmu 			break;
 66 5dc21454 2023-07-14 jrmu 		case '*':
 67 5dc21454 2023-07-14 jrmu 			push(pop() * pop());
 68 5dc21454 2023-07-14 jrmu 			break;
 69 5dc21454 2023-07-14 jrmu 		case '-':
 70 5dc21454 2023-07-14 jrmu 			op2 = pop();
 71 5dc21454 2023-07-14 jrmu 			push(pop() - op2);
 72 5dc21454 2023-07-14 jrmu 			break;
 73 5dc21454 2023-07-14 jrmu 		case '/':
 74 5dc21454 2023-07-14 jrmu 			op2 = pop();
 75 5dc21454 2023-07-14 jrmu 			if (op2 != 0.0)
 76 5dc21454 2023-07-14 jrmu 				push(pop() / op2);
 77 5dc21454 2023-07-14 jrmu 			else
 78 5dc21454 2023-07-14 jrmu 				printf("error: zero divisor\n");
 79 5dc21454 2023-07-14 jrmu 			break;
 80 5dc21454 2023-07-14 jrmu 		case '%':
 81 5dc21454 2023-07-14 jrmu 			op2 = pop();
 82 5dc21454 2023-07-14 jrmu 			if (op2 != 0.0)
 83 5dc21454 2023-07-14 jrmu 				push((int) pop() % (int) op2);
 84 5dc21454 2023-07-14 jrmu 			else
 85 5dc21454 2023-07-14 jrmu 				printf("error: zero divisor\n");
 86 5dc21454 2023-07-14 jrmu 			break;
 87 5dc21454 2023-07-14 jrmu 		case '?':
 88 5dc21454 2023-07-14 jrmu 			printf("\t%.8g\n", printtop());
 89 5dc21454 2023-07-14 jrmu 			break;
 90 5dc21454 2023-07-14 jrmu 		case '#':
 91 5dc21454 2023-07-14 jrmu 			if (duplicate() == 0)
 92 5dc21454 2023-07-14 jrmu 				printf("error: can't duplicate\n");
 93 5dc21454 2023-07-14 jrmu 			break;
 94 5dc21454 2023-07-14 jrmu 		case '~':
 95 5dc21454 2023-07-14 jrmu 			if (swap() == 0)
 96 5dc21454 2023-07-14 jrmu 				printf("error: swap failed, stack needs two numbers\n");
 97 5dc21454 2023-07-14 jrmu 			break;
 98 5dc21454 2023-07-14 jrmu 		case '!':
 99 5dc21454 2023-07-14 jrmu 			clear();
100 5dc21454 2023-07-14 jrmu 			break;
101 5dc21454 2023-07-14 jrmu 		case '\n':
102 5dc21454 2023-07-14 jrmu 			printf("\t%.8g\n", pop());
103 5dc21454 2023-07-14 jrmu 			break;
104 5dc21454 2023-07-14 jrmu 		default:
105 5dc21454 2023-07-14 jrmu 			printf("error: unknown command %s\n", s);
106 5dc21454 2023-07-14 jrmu 			break;
107 5dc21454 2023-07-14 jrmu 		}
108 5dc21454 2023-07-14 jrmu 	}
109 5dc21454 2023-07-14 jrmu }
110 5dc21454 2023-07-14 jrmu 
111 5dc21454 2023-07-14 jrmu #define MAXVAL 100 /* maximum depth of val stack */
112 5dc21454 2023-07-14 jrmu 
113 5dc21454 2023-07-14 jrmu int sp = 0; /* next free stack position */
114 5dc21454 2023-07-14 jrmu double val[MAXVAL]; /* value stack */
115 5dc21454 2023-07-14 jrmu double var[LETTERS]; /* variable stack */
116 5dc21454 2023-07-14 jrmu 
117 5dc21454 2023-07-14 jrmu /* push: push f onto value stack */
118 5dc21454 2023-07-14 jrmu void push (double f) {
119 5dc21454 2023-07-14 jrmu 	if (sp < MAXVAL)
120 5dc21454 2023-07-14 jrmu 		val[sp++] = f;
121 5dc21454 2023-07-14 jrmu 	else
122 5dc21454 2023-07-14 jrmu 		printf ("error: stack full, can't push %g\n", f);
123 5dc21454 2023-07-14 jrmu }
124 5dc21454 2023-07-14 jrmu 
125 5dc21454 2023-07-14 jrmu /* pop: pop and return top value from stack */
126 5dc21454 2023-07-14 jrmu double pop(void) {
127 5dc21454 2023-07-14 jrmu 	if (sp > 0)
128 5dc21454 2023-07-14 jrmu 		return val[--sp];
129 5dc21454 2023-07-14 jrmu 	else {
130 5dc21454 2023-07-14 jrmu 		printf("error: stack empty\n");
131 5dc21454 2023-07-14 jrmu 		return 0.0;
132 5dc21454 2023-07-14 jrmu 	}
133 5dc21454 2023-07-14 jrmu }
134 5dc21454 2023-07-14 jrmu 
135 5dc21454 2023-07-14 jrmu /* printtop: print the top value of the stack without popping it */
136 5dc21454 2023-07-14 jrmu double printtop(void) {
137 5dc21454 2023-07-14 jrmu 	if (sp > 0)
138 5dc21454 2023-07-14 jrmu 		return val[sp-1];
139 5dc21454 2023-07-14 jrmu 	else {
140 5dc21454 2023-07-14 jrmu 		printf("error: stack empty\n");
141 5dc21454 2023-07-14 jrmu 		return 0.0;
142 5dc21454 2023-07-14 jrmu 	}
143 5dc21454 2023-07-14 jrmu }
144 5dc21454 2023-07-14 jrmu 
145 5dc21454 2023-07-14 jrmu /* duplicate: duplicate the top value of the stack
146 5dc21454 2023-07-14 jrmu  * return 1 if successful, 0 on failure */
147 5dc21454 2023-07-14 jrmu int duplicate(void) {
148 5dc21454 2023-07-14 jrmu 	if (sp <= 0) {
149 5dc21454 2023-07-14 jrmu 		return 0;
150 5dc21454 2023-07-14 jrmu 	} else if (sp >= MAXVAL) {
151 5dc21454 2023-07-14 jrmu 		return 0;
152 5dc21454 2023-07-14 jrmu 	} else {
153 5dc21454 2023-07-14 jrmu 		val[sp] = val[sp-1];
154 5dc21454 2023-07-14 jrmu 		sp++;
155 5dc21454 2023-07-14 jrmu 		return 1;
156 5dc21454 2023-07-14 jrmu 	}
157 5dc21454 2023-07-14 jrmu }
158 5dc21454 2023-07-14 jrmu 
159 5dc21454 2023-07-14 jrmu /* swap: swap the top two values of the stack
160 5dc21454 2023-07-14 jrmu  * return 1 if successful, 0 on failure */
161 5dc21454 2023-07-14 jrmu int swap(void) {
162 5dc21454 2023-07-14 jrmu 	if (sp > 1) {
163 5dc21454 2023-07-14 jrmu 		int temp = val[sp-1];
164 5dc21454 2023-07-14 jrmu 		val[sp-1] = val[sp-2];
165 5dc21454 2023-07-14 jrmu 		val[sp-2] = temp;
166 5dc21454 2023-07-14 jrmu 		return 1;
167 5dc21454 2023-07-14 jrmu 	}
168 5dc21454 2023-07-14 jrmu 	return 0;
169 5dc21454 2023-07-14 jrmu }
170 5dc21454 2023-07-14 jrmu 
171 5dc21454 2023-07-14 jrmu /* clear: clear the stack */
172 5dc21454 2023-07-14 jrmu void clear(void) {
173 5dc21454 2023-07-14 jrmu 	sp = 0;
174 5dc21454 2023-07-14 jrmu }
175 5dc21454 2023-07-14 jrmu 
176 5dc21454 2023-07-14 jrmu /* assign: assign a double to a variable, letters represented by int from 0-25
177 5dc21454 2023-07-14 jrmu  * return 1 on success, 0 on failure */
178 5dc21454 2023-07-14 jrmu int assign(int index, double value) {
179 5dc21454 2023-07-14 jrmu 	if (0 <= index && index < LETTERS) {
180 5dc21454 2023-07-14 jrmu 		var[index] = value;
181 5dc21454 2023-07-14 jrmu 		return 1;
182 5dc21454 2023-07-14 jrmu 	}
183 5dc21454 2023-07-14 jrmu 	return 0;
184 5dc21454 2023-07-14 jrmu }
185 5dc21454 2023-07-14 jrmu 
186 5dc21454 2023-07-14 jrmu /* eval: evaluate variable, letters represented by int from 0-25 */
187 5dc21454 2023-07-14 jrmu double eval(int index) {
188 5dc21454 2023-07-14 jrmu 	if (0 <= index && index < LETTERS) {
189 5dc21454 2023-07-14 jrmu 		return var[index];
190 5dc21454 2023-07-14 jrmu 	}
191 5dc21454 2023-07-14 jrmu 	return 0.0;
192 5dc21454 2023-07-14 jrmu }
193 5dc21454 2023-07-14 jrmu 
194 5dc21454 2023-07-14 jrmu #include <ctype.h>
195 5dc21454 2023-07-14 jrmu 
196 5dc21454 2023-07-14 jrmu int getch(void);
197 5dc21454 2023-07-14 jrmu void ungetch(int);
198 5dc21454 2023-07-14 jrmu 
199 5dc21454 2023-07-14 jrmu /* getop: get next operator or numeric operand */
200 5dc21454 2023-07-14 jrmu int getop(char s[]) {
201 5dc21454 2023-07-14 jrmu 	int i;
202 5dc21454 2023-07-14 jrmu 	static int c = ' ';
203 5dc21454 2023-07-14 jrmu 	int op;
204 5dc21454 2023-07-14 jrmu 	while (c == ' ' || c == '\t') {
205 5dc21454 2023-07-14 jrmu 		c = getchar();
206 5dc21454 2023-07-14 jrmu 	}
207 5dc21454 2023-07-14 jrmu 	s[0] = c;
208 5dc21454 2023-07-14 jrmu 	s[1] = '\0';
209 5dc21454 2023-07-14 jrmu 	i = 0;
210 5dc21454 2023-07-14 jrmu 	if (isalpha(c)) {
211 5dc21454 2023-07-14 jrmu 		while ((s[++i] = c = getch()) != ' ' && c != '\t' && c != '\n')
212 5dc21454 2023-07-14 jrmu 			;
213 5dc21454 2023-07-14 jrmu 		s[i] = '\0';
214 5dc21454 2023-07-14 jrmu 		if (s[1] == '=') {
215 5dc21454 2023-07-14 jrmu 			return ASSIGNMENT;
216 5dc21454 2023-07-14 jrmu 		} else if (s[1] == '\0') {
217 5dc21454 2023-07-14 jrmu 			return VARIABLE;
218 5dc21454 2023-07-14 jrmu 		} else {
219 5dc21454 2023-07-14 jrmu 			return IDENTIFIER;
220 5dc21454 2023-07-14 jrmu 		}
221 5dc21454 2023-07-14 jrmu 	}
222 5dc21454 2023-07-14 jrmu 	/* negative number or minus */
223 5dc21454 2023-07-14 jrmu 	if (c == '-') {
224 5dc21454 2023-07-14 jrmu 		s[++i] = c = getch();
225 5dc21454 2023-07-14 jrmu 		if (!isdigit(c) && c != '.') {
226 5dc21454 2023-07-14 jrmu 			return '-';
227 5dc21454 2023-07-14 jrmu 		}
228 5dc21454 2023-07-14 jrmu 	}
229 5dc21454 2023-07-14 jrmu 	if (!isdigit(c) && c != '.') {
230 5dc21454 2023-07-14 jrmu 		op = c;
231 5dc21454 2023-07-14 jrmu 		c = ' ';
232 5dc21454 2023-07-14 jrmu 		return op; /* not a number */
233 5dc21454 2023-07-14 jrmu 	}
234 5dc21454 2023-07-14 jrmu 	if (isdigit(c)) /* collect integer part */
235 5dc21454 2023-07-14 jrmu 		while (isdigit(s[++i] = c = getch()))
236 5dc21454 2023-07-14 jrmu 			;
237 5dc21454 2023-07-14 jrmu 	if (c == '.') /* collect fraction part */
238 5dc21454 2023-07-14 jrmu 		while (isdigit(s[++i] = c = getch()))
239 5dc21454 2023-07-14 jrmu 			;
240 5dc21454 2023-07-14 jrmu 	s[i] = '\0';
241 5dc21454 2023-07-14 jrmu 	return NUMBER;
242 5dc21454 2023-07-14 jrmu }
243 5dc21454 2023-07-14 jrmu 
244 5dc21454 2023-07-14 jrmu #define BUFSIZE 100
245 5dc21454 2023-07-14 jrmu 
246 5dc21454 2023-07-14 jrmu char buf[BUFSIZE]; /* buffer for ungetch */
247 5dc21454 2023-07-14 jrmu int bufp = 0;
248 5dc21454 2023-07-14 jrmu 
249 5dc21454 2023-07-14 jrmu /* get a (possibly pushed back) character */
250 5dc21454 2023-07-14 jrmu int getch(void) {
251 5dc21454 2023-07-14 jrmu 	return (bufp > 0) ? buf[--bufp] : getchar();
252 5dc21454 2023-07-14 jrmu }
253 5dc21454 2023-07-14 jrmu 
254 5dc21454 2023-07-14 jrmu /* push character back on input */
255 5dc21454 2023-07-14 jrmu void ungetch(int c) {
256 5dc21454 2023-07-14 jrmu 	if (bufp >= BUFSIZE)
257 5dc21454 2023-07-14 jrmu 		printf("ungetch: too many characters\n");
258 5dc21454 2023-07-14 jrmu 	else
259 5dc21454 2023-07-14 jrmu 		buf[bufp++] = c;
260 5dc21454 2023-07-14 jrmu }