1 5dc21454 2023-07-14 jrmu /*
  2 5dc21454 2023-07-14 jrmu  * Exercise 4-3. Given the basic framework, it's straightforward to extend the
  3 5dc21454 2023-07-14 jrmu  * calculator. Add the modulus (%) operator and provisions for negative
  4 5dc21454 2023-07-14 jrmu  * numbers.
  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 
 17 5dc21454 2023-07-14 jrmu /* reverse Polish calculator */
 18 5dc21454 2023-07-14 jrmu int main() {
 19 5dc21454 2023-07-14 jrmu 	int type;
 20 5dc21454 2023-07-14 jrmu 	double op2;
 21 5dc21454 2023-07-14 jrmu 	char s[MAXOP];
 22 5dc21454 2023-07-14 jrmu 
 23 5dc21454 2023-07-14 jrmu 	while ((type = getop(s)) != EOF) {
 24 5dc21454 2023-07-14 jrmu 		switch (type) {
 25 5dc21454 2023-07-14 jrmu 		case NUMBER:
 26 5dc21454 2023-07-14 jrmu 			push(atof(s));
 27 5dc21454 2023-07-14 jrmu 			break;
 28 5dc21454 2023-07-14 jrmu 		case '+':
 29 5dc21454 2023-07-14 jrmu 			push(pop() + pop());
 30 5dc21454 2023-07-14 jrmu 			break;
 31 5dc21454 2023-07-14 jrmu 		case '*':
 32 5dc21454 2023-07-14 jrmu 			push(pop() * pop());
 33 5dc21454 2023-07-14 jrmu 			break;
 34 5dc21454 2023-07-14 jrmu 		case '-':
 35 5dc21454 2023-07-14 jrmu 			op2 = pop();
 36 5dc21454 2023-07-14 jrmu 			push(pop() - op2);
 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 			if (op2 != 0.0)
 41 5dc21454 2023-07-14 jrmu 				push(pop() / op2);
 42 5dc21454 2023-07-14 jrmu 			else
 43 5dc21454 2023-07-14 jrmu 				printf("error: zero divisor\n");
 44 5dc21454 2023-07-14 jrmu 			break;
 45 5dc21454 2023-07-14 jrmu 		case '%':
 46 5dc21454 2023-07-14 jrmu 			op2 = pop();
 47 5dc21454 2023-07-14 jrmu 			if (op2 != 0.0)
 48 5dc21454 2023-07-14 jrmu 				push((int) pop() % (int) op2);
 49 5dc21454 2023-07-14 jrmu 			else
 50 5dc21454 2023-07-14 jrmu 				printf("error: zero divisor\n");
 51 5dc21454 2023-07-14 jrmu 			break;
 52 5dc21454 2023-07-14 jrmu 		case '\n':
 53 5dc21454 2023-07-14 jrmu 			printf("\t%.8g\n", pop());
 54 5dc21454 2023-07-14 jrmu 			break;
 55 5dc21454 2023-07-14 jrmu 		default:
 56 5dc21454 2023-07-14 jrmu 			printf("error: unknown command %s\n", s);
 57 5dc21454 2023-07-14 jrmu 			break;
 58 5dc21454 2023-07-14 jrmu 		}
 59 5dc21454 2023-07-14 jrmu 	}
 60 5dc21454 2023-07-14 jrmu }
 61 5dc21454 2023-07-14 jrmu 
 62 5dc21454 2023-07-14 jrmu #define MAXVAL 100 /* maximum depth of val stack */
 63 5dc21454 2023-07-14 jrmu 
 64 5dc21454 2023-07-14 jrmu int sp = 0; /* next free stack position */
 65 5dc21454 2023-07-14 jrmu double val[MAXVAL]; /* value stack */
 66 5dc21454 2023-07-14 jrmu 
 67 5dc21454 2023-07-14 jrmu /* push: push f onto value stack */
 68 5dc21454 2023-07-14 jrmu void push (double f) {
 69 5dc21454 2023-07-14 jrmu 	if (sp < MAXVAL)
 70 5dc21454 2023-07-14 jrmu 		val[sp++] = f;
 71 5dc21454 2023-07-14 jrmu 	else
 72 5dc21454 2023-07-14 jrmu 		printf ("error: stack full, can't push %g\n", f);
 73 5dc21454 2023-07-14 jrmu }
 74 5dc21454 2023-07-14 jrmu 
 75 5dc21454 2023-07-14 jrmu /* pop: pop and return top value from stack */
 76 5dc21454 2023-07-14 jrmu double pop(void) {
 77 5dc21454 2023-07-14 jrmu 	if (sp > 0)
 78 5dc21454 2023-07-14 jrmu 		return val[--sp];
 79 5dc21454 2023-07-14 jrmu 	else {
 80 5dc21454 2023-07-14 jrmu 		printf("error: stack empty\n");
 81 5dc21454 2023-07-14 jrmu 		return 0.0;
 82 5dc21454 2023-07-14 jrmu 	}
 83 5dc21454 2023-07-14 jrmu }
 84 5dc21454 2023-07-14 jrmu 
 85 5dc21454 2023-07-14 jrmu #include <ctype.h>
 86 5dc21454 2023-07-14 jrmu 
 87 5dc21454 2023-07-14 jrmu int getch(void);
 88 5dc21454 2023-07-14 jrmu void ungetch(int);
 89 5dc21454 2023-07-14 jrmu 
 90 5dc21454 2023-07-14 jrmu /* getop: get next operator or numeric operand */
 91 5dc21454 2023-07-14 jrmu int getop(char s[]) {
 92 5dc21454 2023-07-14 jrmu 	int i, c;
 93 5dc21454 2023-07-14 jrmu 	while ((s[0] = c = getch()) == ' ' || c == '\t')
 94 5dc21454 2023-07-14 jrmu 		;
 95 5dc21454 2023-07-14 jrmu 	s[1] = '\0';
 96 5dc21454 2023-07-14 jrmu 	i = 0;
 97 5dc21454 2023-07-14 jrmu 	/* negative number or minus */
 98 5dc21454 2023-07-14 jrmu 	if (c == '-') {
 99 5dc21454 2023-07-14 jrmu 		s[++i] = c = getch();
100 5dc21454 2023-07-14 jrmu 		if (!isdigit(c) && c != '.') {
101 5dc21454 2023-07-14 jrmu 			ungetch(c);
102 5dc21454 2023-07-14 jrmu 			return '-';
103 5dc21454 2023-07-14 jrmu 		}
104 5dc21454 2023-07-14 jrmu 	}
105 5dc21454 2023-07-14 jrmu 	if (!isdigit(c) && c != '.')
106 5dc21454 2023-07-14 jrmu 		return c; /* not a number */
107 5dc21454 2023-07-14 jrmu 	if (isdigit(c)) /* collect integer part */
108 5dc21454 2023-07-14 jrmu 		while (isdigit(s[++i] = c = getch()))
109 5dc21454 2023-07-14 jrmu 			;
110 5dc21454 2023-07-14 jrmu 	if (c == '.') /* collect fraction part */
111 5dc21454 2023-07-14 jrmu 		while (isdigit(s[++i] = c = getch()))
112 5dc21454 2023-07-14 jrmu 			;
113 5dc21454 2023-07-14 jrmu 	s[i] = '\0';
114 5dc21454 2023-07-14 jrmu 	if (c != EOF)
115 5dc21454 2023-07-14 jrmu 		ungetch(c);
116 5dc21454 2023-07-14 jrmu 	return NUMBER;
117 5dc21454 2023-07-14 jrmu }
118 5dc21454 2023-07-14 jrmu 
119 5dc21454 2023-07-14 jrmu #define BUFSIZE 100
120 5dc21454 2023-07-14 jrmu 
121 5dc21454 2023-07-14 jrmu char buf[BUFSIZE]; /* buffer for ungetch */
122 5dc21454 2023-07-14 jrmu int bufp = 0;
123 5dc21454 2023-07-14 jrmu 
124 5dc21454 2023-07-14 jrmu /* get a (possibly pushed back) character */
125 5dc21454 2023-07-14 jrmu int getch(void) {
126 5dc21454 2023-07-14 jrmu 	return (bufp > 0) ? buf[--bufp] : getchar();
127 5dc21454 2023-07-14 jrmu }
128 5dc21454 2023-07-14 jrmu 
129 5dc21454 2023-07-14 jrmu /* push character back on input */
130 5dc21454 2023-07-14 jrmu void ungetch(int c) {
131 5dc21454 2023-07-14 jrmu 	if (bufp >= BUFSIZE)
132 5dc21454 2023-07-14 jrmu 		printf("ungetch: too many characters\n");
133 5dc21454 2023-07-14 jrmu 	else
134 5dc21454 2023-07-14 jrmu 		buf[bufp++] = c;
135 5dc21454 2023-07-14 jrmu }