undefined reference help

ETC Homework & Coursework Questions
1

Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!

  1. The problem statement, all variables and given/known data:
    The problem is a function which i typed although it kept saying that it is a undefined reference still. other function worked fine but the main problem is pinpointing at display.h
driver1.c:(.text+0x11): undefined reference to `write_message'
driver1.c:(.text+0x3c): undefined reference to `write_exp'
driver1.c:(.text+0x4b): undefined reference to `write_char'
driver1.c:(.text+0x68): undefined reference to `write_char'
  1. Relevant commands, code, scripts, algorithms:
    this file is given
/*      File:  display.h
        by:    Tep Dobry
        login: tep
        date:  20 Mar 03
*/

/*  This file contains the prototypes for useful funcitons in display.o
        library  */

#define MYFLUSH(c) while((((c) = getchar()) != '\n') && ((c) != 13));

void write_char(char);
/* This function is given a character and writes it to the display.
        The characters recognized to be written include the digits, '0'..'9',
        the operators, '+', '-', 'x', '/', and '=', the period, '.', and
        the special characters, 'q', ' ', '\n', and '\b'.  The
        special characters are explained in the documentation.
*/

void write_exp(char);
/* This function is given a character and writes it as an exponent to
        the dispaly.  The characters recognized to be written are
        the digits '0'..'9', and the minus sign, '-'.
*/

void write_message(char *);
/* This function is given a string which is written in the center
        of the top line of the display.  It also initializes the
        dispaly.
*/

void write_error(char *);
/* This function is given a string which is written to the bottom line
        of the display and causes the display to beep.
*/

void write_debug(int);
/* This function is given an integer which is written to the bottom line
        of the display to be used as debugging output in the program
*/
  1. The attempts at a solution (include all code and scripts):
main()
{  char ch;

        /*  Initialize the dispaly with a message  */
        write_message("Display Test");

        /*  while not quitting  */
        while((ch = getchar()) != 'q')
        {
                /*  if exponent character */
                if( is_exp(ch))
                        /*  write the converted exponent character  */
                        write_exp(exp_value(ch));
                /*  otherwise write the character  */
                else write_char(ch);
        }

        /* write the q character to terminate the dispaly */
        write_char(ch);

}
  1. Complete Name of School (University), City (State), Country, Name of Professor, and Course Number (Link to Course):
    University of Hawaii at Manoa, Honolulu(HI), Oahu (Hawaii), tep dobry, ee160 EE 160: Homework 4

Note: Without school/professor/course information, you will be banned if you post here! You must complete the entire template (not just parts of it).

2

Where is the code, not the one-line declaration?
for example:

void write_error(char *msg)
{
    fprintf(stderr, "Error msg: %s\n", msg);
}

You have to compile that as well. And

char ch;

is not a pointer to char or a string array either - that is what you are passing to the functions that require char *.

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