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#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#define NUMBER '0'
#define MAXOP 100
#define MAXVAL 100
int getop(char[]);
void push(double);
double pop(void);
/**
* Reverse polish notation calculator
*/
int main(void) {
int type;
double op2;
char s[MAXOP];
while ((type = getop(s)) != EOF) {
switch (type) {
case NUMBER:
push(atof(s));
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 '\n':
printf("\t%.8g\n", pop());
break;
default:
printf("unknown command %s\n", s);
break;
}
}
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;
}
}
int getch(void);
void ungetch(int);
int getop(char s[]) {
int i,c;
// Skip to teh first non-space or tab character
while ((s[0] = c = getch()) == ' ' || c == '\t');
// Then add a null for some reason?
s[1] = '\0';
// if it's not a part of a number, it's an operation
if (!isdigit(c) && c != '.')
return c;
// Integer part
i = 0;
if (isdigit(c))
while (isdigit(s[++i] = c = getch()));
// fraction part
if (c == '.')
while (isdigit(s[++i] = c = getch()));
s[i] = '\0';
if (c != EOF)
ungetch(c);
return NUMBER;
}
#define BUFSIZE 100
char buf[BUFSIZE]; // buffer for ungetch
int bufp = 0; // next free in buf
int getch(void) {
return (bufp > 0) ? buf[--bufp] : getchar();
}
void ungetch(int c) {
if (bufp >= BUFSIZE)
printf("ungetch: buffer full\n");
else
buf[bufp++] = c;
}
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