undefined reference to `fmod'

[musikluvah]

I am going through K&R C Answer Book and coding exercise4-3.c
there is a call for fmod library function which I thought was present in math.h but I am resulting an 'underfined reference to 'fmod'
the line in question is about 3 quarters the way down - just below the case '%': line

any clues what I am doing wrong.

gcc -o exercise4-3.exe exercise4-3.c
/tmp/ccOFQfVw.o: In function `main':
/tmp/ccOFQfVw.o(.text+0x169): undefined reference to `fmod'

gcc -v
Using builtin specs.
gcc version 2.95.4 20020320 [FreeBSD]

#include  <stdio.h>
#include  <math.h>      /* for atof()   */
#include  <ctype.h>     /* for atof()   */
#include  <string.h>

#define    MAXVAL   1000  /* maximum depth  of val stack       */
#define    MAXOP    100   /* max size of operand or operator   */
#define    NUMBER   '0'   /* signal that a number was found    */
#define    BUFSIZE  100


int sp = 0;           /* next free stack position  */
double val[MAXVAL];   /* value stack */
int getop(char []);
void push(double);
double pop(void);
int getch(void);
void ungetch(int);
char buf[BUFSIZE];   /* buffer for ungetch */
int  bufp = 0;       /* next free positino in buf */


double atof(char s[]);

int i, sign;

/* reverse Polish calculator   */
main()
{
  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 divisor\n");
      break;
    case '%':
      op2 = pop();
      if (op2 != 0.0)
        push(fmod(pop(), op2));
      else
        printf("error: zero divisor\n");
      break;   
    case '\n':
      printf("\t%.8g\n", pop());
      break;
    default:
      printf("error: unkown command %s\n", s);
      break;
    }

  }
  return 0;
}

[Dave_Sinkula]

I don't see that. I do see lots of complaint about push and pop and getop.

[cwr]

Append -lm to your command line invocation. gcc tends to need to be told to include the math library.

[musikluvah]

Brilliant cwr - that is the answer!