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#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#define NUMBER '0'
#define MAXLINE 1000
#define MAXVAL 100
int getop(char[]);
void push(double);
double pop(void);
void clear(void);
double peek(void);
// Naïve implementation of remainder operation
double frem(double f1, double f2) {
return f1 - (f2 * (int)(f1 / f2));
}
/**
* Reverse polish notation calculator
*/
int main(int argc, char* argv[]) {
if (argc <= 1) {
fprintf(stderr, "Usage: rpol EXPR...");
return 1;
}
argv++; // Skip program name
double op2;
for (; *argv != NULL; argv++) {
char* tok = *argv;
int type = getop(tok);
switch (type) {
case NUMBER:
push(atof(tok));
break;
case '+':
push(pop() + pop());
break;
case '*':
push(pop() * pop());
break;
case '-':
op2 = pop();
push(pop() - op2);
break;
case '/':
op2 = pop();
if (op2 != 0.0)
push(pop() / op2);
else
printf("error: zero division attempted!\n");
break;
case '%':
op2 = pop();
if (op2 != 0.0)
push(frem(pop(), op2));
else
printf("error: zero division attempted!\n");
break;
case '~':
clear();
break;
default:
printf("unknown command %s\n", tok); // Just ignore it?
break;
}
}
printf("\t%.8g\n", pop());
return 0;
}
int sp; // Stack position
double val[MAXVAL]; // Value stack
void push(double f) {
if (sp < MAXVAL) {
val[sp++] = f;
} else {
printf("error, stack full\n");
}
}
double pop(void) {
if (sp >= 0) {
return val[--sp];
} else {
printf("error, empty stack\n");
return 0.0;
}
}
double peek(void) {
if (sp >= 0) {
return val[sp-1];
} else {
printf("error, empty stack\n");
return 0.0;
}
}
void clear(void) {
sp = 0;
}
int getop(char s[]) {
char c = s[0];
if (!isdigit(c) && c != '.')
return c;
return NUMBER;
}
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