Parsing command-line arguments in C

I’m trying to write a program that can compare two files line by line, word by word, or character by character in C. It has to be able to read in command line options -l, -w, -i or --…

• if the option is -l, it compares the files line by line.
• if the option is -w, it compares the files word by word.
• if the option is --, it automatically assumes that the next argument is the first filename.
• if the option is -i, it compares them in a case insensitive manner.
• defaults to comparing the files character by character.

It’s not supposed to matter how many times the options are input as long as -w and -l aren’t inputted at the same time and there are no more or less than two files.

I don’t even know where to begin with parsing the command line arguments.

So this is the code that I came up with for everything. I haven’t error checked it quite yet, but am I writing things in an overcomplicated manner?

/*
 * Functions to compare files.
 */
int compare_line();
int compare_word();
int compare_char();
int case_insens();

/*
 * Program to compare the information in two files and print message saying
 * whether or not this was successful.
 */
int main(int argc, char* argv[])
{
    /* Loop counter */
    size_t i = 0;

    /* Variables for functions */
    int caseIns = 0;
    int line = 0;
    int word = 0;

    /* File pointers */
    FILE *fp1, *fp2;

    /*
     * Read through command-line arguments for options.
     */
    for (i = 1; i < argc; i++)
    {
        printf("argv[%u] = %s\n", i, argv[i]);
        if (argv[i][0] == '-')
        {
             if (argv[i][1] == 'i')
             {
                 caseIns = 1;
             }
             if (argv[i][1] == 'l')
             {
                 line = 1;
             }
             if (argv[i][1] == 'w')
             {
                 word = 1;
             }
             if (argv[i][1] == '-')
             {
                 fp1 = argv[i][2];
                 fp2 = argv[i][3];
             }
             else
             {
                 printf("Invalid option.");
                 return 2;
             }
        }
        else
        {
           fp1(argv[i]);
           fp2(argv[i][1]);
        }
    }

    /*
     * Check that files can be opened.
     */
    if(((fp1 = fopen(fp1, "rb")) ==  NULL) || ((fp2 = fopen(fp2, "rb")) == NULL))
    {
        perror("fopen()");
        return 3;
    }
    else
    {
        if (caseIns == 1)
        {
            if(line == 1 && word == 1)
            {
                printf("That is invalid.");
                return 2;
            }
            if(line == 1 && word == 0)
            {
                if(compare_line(case_insens(fp1, fp2)) == 0)
                        return 0;
            }
            if(line == 0 && word == 1)
            {
                if(compare_word(case_insens(fp1, fp2)) == 0)
                    return 0;
            }
            else
            {
                if(compare_char(case_insens(fp1,fp2)) == 0)
                    return 0;
            }
        }
        else
        {
            if(line == 1 && word == 1)
            {
                printf("That is invalid.");
                return 2;
            }
            if(line == 1 && word == 0)
            {
                if(compare_line(fp1, fp2) == 0)
                    return 0;
            }
            if(line == 0 && word == 1)
            {
                if(compare_word(fp1, fp2) == 0)
                    return 0;
            }