New to C and forum, need some help!
Hello everyone!
After completing most of my undergraduate computer science classes in java/c++, I decided that I wanted to teach myself C. After talking to a few profs and consulting the great internet, I settled upon "The C Programming Language 2nd Ed" by K&R, as it comes highly recommended. I've been reading/doing all of the exercises in my spare time, and I've finally come to a problem I just cannot figure out. It's exercise 4-3 for anyone with the book, but here's my code:
Code:
//Ex4_3-10.c
//Adrian K.
//2/7/09
/* This program contains exercises 4-3 through 4-10. I seriously
* considered skipping this program as the section is about external
* variables, but i realized the program itself is about organization
* of programs in c, which is different than any other language i've
* seen */
#include <stdlib.h> /* for atof() */
#include <stdio.h>
#include <ctype.h>
#include <math.h>
#define MAXOP 100 /* max size of operand or operator */
#define NUMBER 0 /* signal that a number was found */
#define MAXVAL 100 /* maximum depth of val stack */
#define BUFSIZE 100 /*max buffer size for ungetch
int get_top(char s[]);
void push(double f);
double pop(void);
/* reverse Polish calculator */
int main(void)
{
int type;
double op2;
char s[MAXOP];
while ((type = get_top(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 divisor\n");
break;
case '\n':
printf("\t%.8g\n", pop());
break;
default:
printf("error: unknown command %s\n", s);
break;
}
}
return 0;
}
int sp = 0; /* next free stack position */
double val[MAXVAL]; /* value stack */
/* push: push f onto value stack */
void push(double f)
{
if (sp < MAXVAL)
val[sp++] = f;
else
printf("error: stack full, can't push %g\n", f);
}
/* pop: pop and return top value from stack */
double pop(void)
{
if (sp > 0)
return val[--sp];
else {
printf("error: stack empty\n");
return 0.0;
}
}
int getch(void);
void ungetch(int);
/* getop: get next character or numeric operand */
int get_top(char s[])
{
int i, c;
while ((s[0] = c = getch()) == ' ' || c == '\t')
;
s[1] = '\0';
if (!isdigit(c) && c != '.')
return c; /* not a number */
i = 0;
if (isdigit(c)) /* collect integer part */
while (isdigit(s[++i] = c = getch()))
;
if (c == '.') /* collect fraction part */
while (isdigit(s[++i] = c = getch()))
;
s[i] = '\0';
if (c != EOF)
ungetch(c);
return NUMBER;
}
char buf[BUFSIZE]; /* buffer for ungetch */
int bufp = 0; /* next free position in buf */
int getch(void) /* get a (possibly pushed-back) character */
{
return (bufp > 0) ? buf[--bufp] : getchar();
}
void ungetch(int c) /* push character back on input */
{
if (bufp >= BUFSIZE)
printf("ungetch: too many characters\n");
else
buf[bufp++] = c;
}
I haven't even started the exercise, I'm just putting together the code provided in the book, and here's the warnings/errors I'm getting:
Code:
{cs2:~/test} cc Ex4_3-10.c -o Ex4_3-10.out -lm
"Ex4_3-10.c", line 30: warning: implicit function declaration: get_top
"Ex4_3-10.c", line 33: warning: implicit function declaration: push
"Ex4_3-10.c", line 36: warning: implicit function declaration: pop
"Ex4_3-10.c", line 68: identifier redeclared: push
current : function(double) returning void
previous: function() returning int : "Ex4_3-10.c", line 33
"Ex4_3-10.c", line 77: identifier redeclared: pop
current : function(void) returning double
previous: function() returning int : "Ex4_3-10.c", line 36
cc: acomp failed for Ex4_3-10.c
I can't figure out what's wrong with my declaration of push()/pop(), and why nothing is wrong with get_top(). I'm sure it's something really easy but I've been stuck for hours and any help would be greatly appreciated!
