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