debug problem --> chapter 5.6 K&R

Code:

#include <stdio.h>
#include <string.h>
#define MAXLINES 5000 /* max #lines to be sorted */
char *lineptr[MAXLINES]; /* pointers to text lines */
int readlines(char *lineptr[], int nlines);
void writelines(char *lineptr[], int nlines);
void qsort(char *lineptr[], int left, int right);
/* sort input lines */
main()
{
	int nlines; /* number of input lines read */
	if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
		qsort(lineptr, 0, nlines-1);
		writelines(lineptr, nlines);
		return 0;
	} else {
		printf("error: input too big to sort\n");
		return 1;
	}
}
#define MAXLEN 1000 /* max length of any input line */
int getline(char *, int);
char *alloc(int);
/* readlines: read input lines */
int readlines(char *lineptr[], int maxlines)
{
	int len, nlines;
	char *p, line[MAXLEN];
	nlines = 0;
	while ((len = getline(line, MAXLEN)) > 0)
		if (nlines >= maxlines || (p = alloc(len)) == NULL)
			return -1;
		else {
			line[len-1] = '\0'; /* delete newline */
			strcpy(p, line);
			lineptr[nlines++] = p;
		}
	return nlines;
}
/* writelines: write output lines */
void writelines(char *lineptr[], int nlines)
{
	int i;
	for (i = 0; i < nlines; i++)
		printf("%s\n", lineptr[i]);
}

Could you please help me out why I cannot debug? How to do so...

I get these two errors:
"_alloc", referenced from:
"_getline", referenced from:

Looking forward to your answers!

As far as I can tell, it looks like you don't have alloc() or getline() anywhere in your source. But you call these functions, so they need to be included as a preprocessor directive or directly in the source.

done! thanks