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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:
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://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 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!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
