/*PROGRAM TO PRINT THE LAST 'n' LINES OF INPUT
 *CHECKLILST:
 *  -stores the lines as an array of pointers
 *  -accepts n from the command line
 */

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

#define SIZE 100    /*maximum no. of characters in each line*/
#define DMAX 5      /*default value of no. lines to print*/

void readlines(int *, int *, char **);
void printlines(int *, int *, char **);

int main(int argc, char *argv[])
{
    int start= 0; /*stores the location of the oldest line read*/
    int n= (argc==1)?DMAX:atoi(argv[1]+1);
            printf("Value of n is %dnn", n);
    char *line[n];
    int i;
    for(i=0; i<n; i++)
        line[i]= NULL;
    readlines(&start, &n, line);
    printlines(&start, &n, line);
    return EXIT_SUCCESS;
}

/*readlines(): reads lines from a file and stores it as required*/
void readlines(int *start, int *n, char *line[])
{
    char cline[SIZE];
    printf("Enter the name of the filen");
    char filename[20];
    scanf("%s", filename);
    FILE *fin= fopen(filename, "r");

    int i= 0;
    while(fgets(cline, SIZE, fin)) {
        if(line[i%*n]!=NULL)
            free(line[i%*n]);
        line[i%*n]= strdup(cline);

        ++i;

        if(*start+1==*n) {
            *start= 0;
            continue;
        }
        if(i>=*n)
            ++*start;
    }
    --*start;   /*compensate for the extra updation*/
    fclose(fin);
}

/*printlines(): prints the lines*/
void printlines(int *start, int *n, char *line[])
{
    int i=*start;
    do {
        printf("%d. %sn", i, line[i]);
        if(i==*n-1)
            i= 0;
        else
            ++i;
    }
    while(i!=*start && line[i]!=NULL);
}

do {
        printf("%d. %sn", i, line[i]);
        if(i==*n-1)
            i= 0;
        else
            ++i;
    }