sem4-problem2

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#define MAX_INPUT_SIZE 100
#define MAX_STR_LEN 100
#define DEFAULT_N 10

void printHelpAndQuit()
{
    printf("This little useful program can print the last N lines of your input!\n");
    printf("-n\tspecify number of lines to print (%d by default)\n", DEFAULT_N);
    printf("-f\tspecify the file to read from\n");
    printf("-h\tprint this message\n");
    exit(0);
}

int main(int argc, char const *argv[])
{
    char s[MAX_INPUT_SIZE][MAX_STR_LEN];
    int n = 10, i = 0, j = 0;
    FILE *f = stdin;

    for (i = 1; i < argc; i++)
    {
        if (strcmp(argv[i], "-f") == 0)
        {
            // Read from file
            if (i + 1 < argc)
            {
                //Try open file
                if ((f = fopen(argv[++i], "r")) == NULL)
                {
                    printf("Error: Can not read file\n");
                    printHelpAndQuit();
                }
            }
            else
            {
                printf("Error: Specify file name\n");
                printHelpAndQuit();
            }
        }
        else if (strcmp(argv[i], "-n") == 0)
        {
            //Redefine number of lines to print
            if (i + 1 < argc)
            {
                char *pEnd;
                n = strtol(argv[i + 1], &pEnd, 10);
                if (pEnd == argv[i + 1])
                {
                    printf("Error: Argument -n is not valid number\n");
                    printHelpAndQuit();
                }
                i++;
            }
            else
            {
                printf("Error: Specify number of lines to print after -n\n");
                printHelpAndQuit();
            }
        }
        else if (strcmp(argv[i], "-h") == 0)
        {
            printHelpAndQuit();
        }
        else
        {
            printf("Invalid parameter\n");
            printHelpAndQuit();
        }
    }

    i = 0;
    while (fscanf(f, "%s", s[i++]) != EOF);

    printf("\n");
    if (n > i - 1)
        printf("Too many lines to print!\n");
    else
        for (j = i - n - 1; j < i; j++)
            printf("%s\n", s[j]);

    fclose(f);
    return 0;
}