1 5dc21454 2023-07-14 jrmu /*
  2 5dc21454 2023-07-14 jrmu  * Exercise 4-4. Add commands to print the top element of the stack without
  3 5dc21454 2023-07-14 jrmu  * popping, to duplicate it, and to swap the top two elements. Add a command to
  4 5dc21454 2023-07-14 jrmu  * clear the stack.
  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 
 10 5dc21454 2023-07-14 jrmu #define MAXOP 100 /* max size of operand or operator */
 11 5dc21454 2023-07-14 jrmu #define NUMBER '0' /* signal that a number was found */
 12 5dc21454 2023-07-14 jrmu 
 13 5dc21454 2023-07-14 jrmu int getop(char []);
 14 5dc21454 2023-07-14 jrmu void push(double);
 15 5dc21454 2023-07-14 jrmu double pop(void);
 16 5dc21454 2023-07-14 jrmu double printtop(void);
 17 5dc21454 2023-07-14 jrmu int duplicate(void);
 18 5dc21454 2023-07-14 jrmu int swap(void);
 19 5dc21454 2023-07-14 jrmu void clear(void);
 20 5dc21454 2023-07-14 jrmu 
 21 5dc21454 2023-07-14 jrmu /* reverse Polish calculator */
 22 5dc21454 2023-07-14 jrmu int main() {
 23 5dc21454 2023-07-14 jrmu 	int type;
 24 5dc21454 2023-07-14 jrmu 	double op2;
 25 5dc21454 2023-07-14 jrmu 	char s[MAXOP];
 26 5dc21454 2023-07-14 jrmu 
 27 5dc21454 2023-07-14 jrmu 	while ((type = getop(s)) != EOF) {
 28 5dc21454 2023-07-14 jrmu 		switch (type) {
 29 5dc21454 2023-07-14 jrmu 		case NUMBER:
 30 5dc21454 2023-07-14 jrmu 			push(atof(s));
 31 5dc21454 2023-07-14 jrmu 			break;
 32 5dc21454 2023-07-14 jrmu 		case '+':
 33 5dc21454 2023-07-14 jrmu 			push(pop() + pop());
 34 5dc21454 2023-07-14 jrmu 			break;
 35 5dc21454 2023-07-14 jrmu 		case '*':
 36 5dc21454 2023-07-14 jrmu 			push(pop() * pop());
 37 5dc21454 2023-07-14 jrmu 			break;
 38 5dc21454 2023-07-14 jrmu 		case '-':
 39 5dc21454 2023-07-14 jrmu 			op2 = pop();
 40 5dc21454 2023-07-14 jrmu 			push(pop() - op2);
 41 5dc21454 2023-07-14 jrmu 			break;
 42 5dc21454 2023-07-14 jrmu 		case '/':
 43 5dc21454 2023-07-14 jrmu 			op2 = pop();
 44 5dc21454 2023-07-14 jrmu 			if (op2 != 0.0)
 45 5dc21454 2023-07-14 jrmu 				push(pop() / op2);
 46 5dc21454 2023-07-14 jrmu 			else
 47 5dc21454 2023-07-14 jrmu 				printf("error: zero divisor\n");
 48 5dc21454 2023-07-14 jrmu 			break;
 49 5dc21454 2023-07-14 jrmu 		case '%':
 50 5dc21454 2023-07-14 jrmu 			op2 = pop();
 51 5dc21454 2023-07-14 jrmu 			if (op2 != 0.0)
 52 5dc21454 2023-07-14 jrmu 				push((int) pop() % (int) op2);
 53 5dc21454 2023-07-14 jrmu 			else
 54 5dc21454 2023-07-14 jrmu 				printf("error: zero divisor\n");
 55 5dc21454 2023-07-14 jrmu 			break;
 56 5dc21454 2023-07-14 jrmu 		case '?':
 57 5dc21454 2023-07-14 jrmu 			printf("\t%.8g\n", printtop());
 58 5dc21454 2023-07-14 jrmu 			break;
 59 5dc21454 2023-07-14 jrmu 		case '#':
 60 5dc21454 2023-07-14 jrmu 			if (duplicate() == 0)
 61 5dc21454 2023-07-14 jrmu 				printf("error: can't duplicate\n");
 62 5dc21454 2023-07-14 jrmu 			break;
 63 5dc21454 2023-07-14 jrmu 		case '~':
 64 5dc21454 2023-07-14 jrmu 			if (swap() == 0)
 65 5dc21454 2023-07-14 jrmu 				printf("error: swap failed, stack needs two numbers\n");
 66 5dc21454 2023-07-14 jrmu 			break;
 67 5dc21454 2023-07-14 jrmu 		case '!':
 68 5dc21454 2023-07-14 jrmu 			clear();
 69 5dc21454 2023-07-14 jrmu 			break;
 70 5dc21454 2023-07-14 jrmu 		case '\n':
 71 5dc21454 2023-07-14 jrmu 			printf("\t%.8g\n", pop());
 72 5dc21454 2023-07-14 jrmu 			break;
 73 5dc21454 2023-07-14 jrmu 		default:
 74 5dc21454 2023-07-14 jrmu 			printf("error: unknown command %s\n", s);
 75 5dc21454 2023-07-14 jrmu 			break;
 76 5dc21454 2023-07-14 jrmu 		}
 77 5dc21454 2023-07-14 jrmu 	}
 78 5dc21454 2023-07-14 jrmu }
 79 5dc21454 2023-07-14 jrmu 
 80 5dc21454 2023-07-14 jrmu #define MAXVAL 100 /* maximum depth of val stack */
 81 5dc21454 2023-07-14 jrmu 
 82 5dc21454 2023-07-14 jrmu int sp = 0; /* next free stack position */
 83 5dc21454 2023-07-14 jrmu double val[MAXVAL]; /* value stack */
 84 5dc21454 2023-07-14 jrmu 
 85 5dc21454 2023-07-14 jrmu /* push: push f onto value stack */
 86 5dc21454 2023-07-14 jrmu void push (double f) {
 87 5dc21454 2023-07-14 jrmu 	if (sp < MAXVAL)
 88 5dc21454 2023-07-14 jrmu 		val[sp++] = f;
 89 5dc21454 2023-07-14 jrmu 	else
 90 5dc21454 2023-07-14 jrmu 		printf ("error: stack full, can't push %g\n", f);
 91 5dc21454 2023-07-14 jrmu }
 92 5dc21454 2023-07-14 jrmu 
 93 5dc21454 2023-07-14 jrmu /* pop: pop and return top value from stack */
 94 5dc21454 2023-07-14 jrmu double pop(void) {
 95 5dc21454 2023-07-14 jrmu 	if (sp > 0)
 96 5dc21454 2023-07-14 jrmu 		return val[--sp];
 97 5dc21454 2023-07-14 jrmu 	else {
 98 5dc21454 2023-07-14 jrmu 		printf("error: stack empty\n");
 99 5dc21454 2023-07-14 jrmu 		return 0.0;
100 5dc21454 2023-07-14 jrmu 	}
101 5dc21454 2023-07-14 jrmu }
102 5dc21454 2023-07-14 jrmu 
103 5dc21454 2023-07-14 jrmu /* printtop: print the top value of the stack without popping it */
104 5dc21454 2023-07-14 jrmu double printtop(void) {
105 5dc21454 2023-07-14 jrmu 	if (sp > 0)
106 5dc21454 2023-07-14 jrmu 		return val[sp-1];
107 5dc21454 2023-07-14 jrmu 	else {
108 5dc21454 2023-07-14 jrmu 		printf("error: stack empty\n");
109 5dc21454 2023-07-14 jrmu 		return 0.0;
110 5dc21454 2023-07-14 jrmu 	}
111 5dc21454 2023-07-14 jrmu }
112 5dc21454 2023-07-14 jrmu 
113 5dc21454 2023-07-14 jrmu /* duplicate: duplicate the top value of the stack
114 5dc21454 2023-07-14 jrmu  * return 1 if successful, 0 on failure */
115 5dc21454 2023-07-14 jrmu int duplicate(void) {
116 5dc21454 2023-07-14 jrmu 	if (sp <= 0) {
117 5dc21454 2023-07-14 jrmu 		return 0;
118 5dc21454 2023-07-14 jrmu 	} else if (sp >= MAXVAL) {
119 5dc21454 2023-07-14 jrmu 		return 0;
120 5dc21454 2023-07-14 jrmu 	} else {
121 5dc21454 2023-07-14 jrmu 		val[sp] = val[sp-1];
122 5dc21454 2023-07-14 jrmu 		sp++;
123 5dc21454 2023-07-14 jrmu 		return 1;
124 5dc21454 2023-07-14 jrmu 	}
125 5dc21454 2023-07-14 jrmu }
126 5dc21454 2023-07-14 jrmu 
127 5dc21454 2023-07-14 jrmu /* swap: swap the top two values of the stack
128 5dc21454 2023-07-14 jrmu  * return 1 if successful, 0 on failure */
129 5dc21454 2023-07-14 jrmu int swap(void) {
130 5dc21454 2023-07-14 jrmu 	if (sp > 1) {
131 5dc21454 2023-07-14 jrmu 		int temp = val[sp-1];
132 5dc21454 2023-07-14 jrmu 		val[sp-1] = val[sp-2];
133 5dc21454 2023-07-14 jrmu 		val[sp-2] = temp;
134 5dc21454 2023-07-14 jrmu 		return 1;
135 5dc21454 2023-07-14 jrmu 	}
136 5dc21454 2023-07-14 jrmu 	return 0;
137 5dc21454 2023-07-14 jrmu }
138 5dc21454 2023-07-14 jrmu 
139 5dc21454 2023-07-14 jrmu /* clear: clear the stack */
140 5dc21454 2023-07-14 jrmu void clear(void) {
141 5dc21454 2023-07-14 jrmu 	sp = 0;
142 5dc21454 2023-07-14 jrmu }
143 5dc21454 2023-07-14 jrmu 
144 5dc21454 2023-07-14 jrmu #include <ctype.h>
145 5dc21454 2023-07-14 jrmu 
146 5dc21454 2023-07-14 jrmu int getch(void);
147 5dc21454 2023-07-14 jrmu void ungetch(int);
148 5dc21454 2023-07-14 jrmu 
149 5dc21454 2023-07-14 jrmu /* getop: get next operator or numeric operand */
150 5dc21454 2023-07-14 jrmu int getop(char s[]) {
151 5dc21454 2023-07-14 jrmu 	int i, c;
152 5dc21454 2023-07-14 jrmu 	while ((s[0] = c = getch()) == ' ' || c == '\t')
153 5dc21454 2023-07-14 jrmu 		;
154 5dc21454 2023-07-14 jrmu 	s[1] = '\0';
155 5dc21454 2023-07-14 jrmu 	i = 0;
156 5dc21454 2023-07-14 jrmu 	/* negative number or minus */
157 5dc21454 2023-07-14 jrmu 	if (c == '-') {
158 5dc21454 2023-07-14 jrmu 		s[++i] = c = getch();
159 5dc21454 2023-07-14 jrmu 		if (!isdigit(c) && c != '.') {
160 5dc21454 2023-07-14 jrmu 			ungetch(c);
161 5dc21454 2023-07-14 jrmu 			return '-';
162 5dc21454 2023-07-14 jrmu 		}
163 5dc21454 2023-07-14 jrmu 	}
164 5dc21454 2023-07-14 jrmu 	if (!isdigit(c) && c != '.')
165 5dc21454 2023-07-14 jrmu 		return c; /* not a number */
166 5dc21454 2023-07-14 jrmu 	if (isdigit(c)) /* collect integer part */
167 5dc21454 2023-07-14 jrmu 		while (isdigit(s[++i] = c = getch()))
168 5dc21454 2023-07-14 jrmu 			;
169 5dc21454 2023-07-14 jrmu 	if (c == '.') /* collect fraction part */
170 5dc21454 2023-07-14 jrmu 		while (isdigit(s[++i] = c = getch()))
171 5dc21454 2023-07-14 jrmu 			;
172 5dc21454 2023-07-14 jrmu 	s[i] = '\0';
173 5dc21454 2023-07-14 jrmu 	if (c != EOF)
174 5dc21454 2023-07-14 jrmu 		ungetch(c);
175 5dc21454 2023-07-14 jrmu 	return NUMBER;
176 5dc21454 2023-07-14 jrmu }
177 5dc21454 2023-07-14 jrmu 
178 5dc21454 2023-07-14 jrmu #define BUFSIZE 100
179 5dc21454 2023-07-14 jrmu 
180 5dc21454 2023-07-14 jrmu char buf[BUFSIZE]; /* buffer for ungetch */
181 5dc21454 2023-07-14 jrmu int bufp = 0;
182 5dc21454 2023-07-14 jrmu 
183 5dc21454 2023-07-14 jrmu /* get a (possibly pushed back) character */
184 5dc21454 2023-07-14 jrmu int getch(void) {
185 5dc21454 2023-07-14 jrmu 	return (bufp > 0) ? buf[--bufp] : getchar();
186 5dc21454 2023-07-14 jrmu }
187 5dc21454 2023-07-14 jrmu 
188 5dc21454 2023-07-14 jrmu /* push character back on input */
189 5dc21454 2023-07-14 jrmu void ungetch(int c) {
190 5dc21454 2023-07-14 jrmu 	if (bufp >= BUFSIZE)
191 5dc21454 2023-07-14 jrmu 		printf("ungetch: too many characters\n");
192 5dc21454 2023-07-14 jrmu 	else
193 5dc21454 2023-07-14 jrmu 		buf[bufp++] = c;
194 5dc21454 2023-07-14 jrmu }