'tail -n' implemented by C

mytail.c

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#define DEFLINES 10
#define MAXLEN   100

int getlines(char *s, int len){
	int c, i;

	for(i = 0; i< len -1 &&(c = getchar()) != EOF && c != '\n'; ++i){
		s[i] = c;
	}

	if(c == '\n'){
		s[i] = c;
		++i;
	}

	s[i] = '\0';

	return i;
}

void show_result(char **res, int end, int total,int isfull)
{
	int i;
	
	if(isfull == 0){
		for( i = 0; i< end; i++)
			printf("%s",res[i]);
	}else{
		if(end == total){
			for(i = 0; i < end; i++)
				printf("%s",res[i]);
		}else{
			for(i = end; i<total; i++)
				printf("%s",res[i]);
			for(i = 0; i< end; i++){
				printf("%s",res[i]);
			}
		}
	}

}



int main(int argc,char **argv){
	char **lineptr;       //save the result
	char line[MAXLEN];    //save the readline
	int  end;			  //the actually end
	int  total;           //total line
	int  len; 
	int  isfull;

	if(argc == 1){
		total = DEFLINES;
	}else if(argc == 2 && (*++argv)[0] == '-'){
		total = atoi(argv[0]+1);
	}else{
		printf("Usage: tail [-n]");
		exit(1);
	}
	
	lineptr = malloc(sizeof(char *) * total);
	end = 0;
	isfull = 0;

	while((len = getlines(line,MAXLEN)) > 0){
		if(end <= total){
			lineptr[end] = malloc(sizeof(char) * len);
			strcpy(lineptr[end], line);
			end++;
		}else{
			end = 0;
			isfull = 1;
			lineptr[end] = malloc(sizeof(char) * len);
			strcpy(lineptr[end],line);
			end++;
		}
	}

	show_result(lineptr,end, total,isfull);
	
	return 0;
}