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#include <ctype.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXOP 100
#define HEIGHT 1000
#define BUFSIZE 100
#define NUM '0'
#define FUN '1'
#define VAR '2'
#define INDEX(x) (x <= 'Z' ? x - 'A' : x - 71) /* index of the variable */
double var[52];
double lout = 0.0;
void clear();
double pop();
double peek();
int getop(char[]);
void push(double);
/* Stack based reverse Polish notation calculator without ungetch()
- single uppercase and lowercase characters are variables (syntax 2 A =);
- special variable LOUT for the last printed value.
- mathematical functions: sin, cos, tan, exp, pow.
- custom functions: swp (swap top 2 values), dup (duplicate last value),
top (peek at the stack top), cls (clear stack).
- operators: +, -, *, /, % and =.
- press enter to print the value at the top of the stack.
*/
int main(int argc, char *argv[]) {
int type;
double op1, op2;
char s[MAXOP];
while ((type = getop(s)) != 0) {
switch (type) {
case NUM:
push(atof(s));
break;
case '+':
op1 = pop();
op2 = pop();
push(op1 + op2);
break;
case '-':
op2 = pop();
op1 = pop();
push(op1 - op2);
break;
case '*':
op2 = pop();
op1 = pop();
push(op1 * op2);
break;
case '/':
op2 = pop();
op1 = pop();
if (op1 == 0.0)
printf("error: division by zero\n");
else
push((double)op1 / op2);
break;
case '%':
op2 = pop();
op1 = pop();
if (op2 == 0.0)
printf("error: division by zero\n");
else
push((int)op1 % (int)op2);
break;
case '=':
var[INDEX(s[0])] = pop();
break;
case VAR:
if (strcmp("LOUT", s) == 0)
push(lout);
else
push(var[INDEX(s[0])]);
break;
case FUN:
if (strcmp("sin", s) == 0)
push(sin(pop()));
else if (strcmp("cos", s) == 0)
push(cos(pop()));
else if (strcmp("tan", s) == 0)
push(tan(pop()));
else if (strcmp("exp", s) == 0)
push(exp(pop()));
else if (strcmp("pow", s) == 0)
push(pow(pop(), pop()));
else if (strcmp("cls", s) == 0)
clear();
else if (strcmp("top", s) == 0) {
lout = peek();
printf("\t%.8g\n", lout);
} else if (strcmp("swp", s) == 0) {
op2 = pop();
op1 = pop();
push(op2);
push(op1);
} else if (strcmp("dup", s) == 0)
push(peek());
else
printf("error: unknown function %s\n", s);
break;
case '\n':
lout = pop();
printf("\t%.8g\n", lout);
break;
default:
printf("error: unknown command %s\n", s);
}
}
return 0;
}
int bufp = 0;
char buf[BUFSIZE];
int getch() { return (bufp > 0) ? buf[--bufp] : getchar(); }
int getop(char s[]) {
int c, i, rc;
static int pc = ' ';
if (pc != ' ' && pc != '\t') {
s[0] = c = pc;
s[1] = 0;
pc = ' ';
} else {
while ((s[0] = c = getch()) == ' ' || c == '\t')
;
s[1] = 0;
}
// special characters and operators
if (c == '+' || c == '*' || c == '/' || c == '%' || c == '\n' || c == EOF)
return c;
i = 0;
if (isdigit(c) || c == '.' || c == '-') {
while (isdigit(s[++i] = c = getch()) || c == '.')
;
pc = c;
rc = i == 1 && s[0] == '-' ? '-' : NUM;
} else {
while (isalnum(s[++i] = c = getch()))
;
s[i] = 0;
if (i == 1) {
if (c == '=' || (c = getch()) == '=')
rc = '=';
else {
pc = c;
rc = VAR;
}
} else {
pc = c;
rc = strcmp("LOUT", s) == 0 ? VAR : FUN;
}
}
s[i] = 0;
return rc;
}
int sp = 0;
double stack[HEIGHT];
void push(double f) {
if (sp < HEIGHT)
stack[sp++] = f;
else
printf("error: stack empty\n");
}
double pop() {
if (sp > 0)
return stack[--sp];
else {
printf("error: stack empty\n");
return 0.0;
}
}
double peek() {
if (sp > 0)
return stack[sp - 1];
else {
printf("error: stack empty\n");
return 0.0;
}
}
void clear() {
for (; sp > 0; sp--)
;
}
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