resize More Comfortable [almost]

/**
 * Resizes a BMP image by n-factor
 */

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

#include "bmp.h"

int main(int argc, char *argv[])
{
    // ensure proper usage
    if (argc != 4)
    {
        fprintf(stderr, "Usage: ./resize n infile outfile\n");
        return 1;
    }

    // remember filenames
    float n = atof(argv[1]);
    char *infile = argv[2];
    char *outfile = argv[3];

    // check if n value in range
    if (n < 0.0 || n > 100.0)
    {
        fprintf(stderr, "n value out of range! [0.0-100.0]\n");
        return 2;
    }

    // open input file
    FILE *inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        fprintf(stderr, "Could not open %s.\n", infile);
        return 3;
    }

    // open output file
    FILE *outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "Could not create %s.\n", outfile);
        return 4;
    }

    // read infile's BITMAPFILEHEADER
    BITMAPFILEHEADER bf;
    fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);

    // read infile's BITMAPINFOHEADER
    BITMAPINFOHEADER bi;
    fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr);

    // ensure infile is (likely) a 24-bit uncompressed BMP 4.0
    if (bf.bfType != 0x4d42 || bf.bfOffBits != 54 || bi.biSize != 40 ||
        bi.biBitCount != 24 || bi.biCompression != 0)
    {
        fclose(outptr);
        fclose(inptr);
        fprintf(stderr, "Unsupported file format.\n");
        return 5;
    }

    // determine padding for scanlines of infile
    int og_padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    // keep infile's width, height
    LONG og_biWidth = bi.biWidth,
        og_biHeight = bi.biHeight;

    // allocate memory for scanline pixels(array of RGBTRIPLE)
    RGBTRIPLE *rgb_array = malloc(og_biWidth * sizeof(RGBTRIPLE));

    // calculate outfile's header parameters
    bi.biWidth *= n;
    bi.biHeight *= n;

    // determine padding for scanlines of outfile
    int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    // calculate rest of outfile's header parameters
    bi.biSizeImage = abs(bi.biHeight) * (bi.biWidth * sizeof(RGBTRIPLE) + padding);
    bf.bfSize = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER) + bi.biSizeImage;


    // write outfile's BITMAPFILEHEADER
    fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, outptr);

    // write outfile's BITMAPINFOHEADER
    fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, outptr);

    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(og_biHeight); i < biHeight; i++)
    {
        printf("\n\ncurrent scanline: %d\n\n", i);
        // write horizontal scanlines n-times (vertical resize)
        for (int v_row = 0; v_row < n; v_row++)
        {
            if (v_row > 0)
                printf("\n\nCopied %i scanline\n\n", i);

                printf("new rgb_array loaded:\n");
            // read scanline's RGB triples from infile to rgb_array
            for (int pixel = 0; pixel < og_biWidth; pixel++)
            {
                fread(&rgb_array[pixel], sizeof(RGBTRIPLE), 1, inptr);
                printf("pixel %d: %x ", pixel, rgb_array[pixel].rgbtRed);
                printf("%x ", rgb_array[pixel].rgbtGreen);
                printf("%x\n", rgb_array[pixel].rgbtBlue);
            }

            // iterate over pixels in scanline
            for (int j = 0; j < og_biWidth; j++)
            {
                // write horizontal scanline n-times (resize)
                for (int h_row = 0; h_row < n; h_row++)
                {
                    printf("J = %d\n", j);
                    // if n has a decimal point
                    if (fmod(n, 1)!= 0)
                    {
                        // first pixel is always the first pixel from scanline
                        if (j == 0)
                        {
                            printf("First (%d) pixel of scanline written.\n", j);
                            fwrite(&rgb_array[j], sizeof(RGBTRIPLE), 1, outptr);
                        }

                        // if n is bigger than 1 - bmp has more pixels, so rewrite last row for each pixel in scanline
                        if (n > 1)
                        {
                            // only write enough pixels to fill extended scanline
                            if (j < bi.biWidth)
                            {
                                printf("Write %dTH  pixel of scanline (rgb_array = %d)\n", j+1, j);
                                fwrite(&rgb_array[j], sizeof(RGBTRIPLE), 1, outptr);
                            }
                        }
                        // else if n less than 1
                        else
                        {
                            // only write enough pixels to fill shrunk scanline
                            if (j < bi.biWidth)
                            {
                                printf("%d pixel: value %d of rgb_array\n", j+1, j+2);
                                fwrite(&rgb_array[j + 2], sizeof(RGBTRIPLE), 1, outptr);
                            }
                        }
                    }
                    else
                    {
                        printf("Wrote normally\n");
                        fwrite(&rgb_array[j], sizeof(RGBTRIPLE), 1, outptr);
                    }
                }
            }

            // skip over og_padding, if any
            fseek(inptr, og_padding, SEEK_CUR);

            // then add it back (to demonstrate how)
            for (int k = 0; k < padding; k++)
            {
                fputc(0x00, outptr);
            }

            // go back with seeker for vertical resizing of scanlines
            if (v_row < n - 1)
            {
              fseek(inptr, -(abs(og_biWidth) * (int)sizeof(RGBTRIPLE) + og_padding), SEEK_CUR);
            }
        }
    }

    // free memory of rgb_array
    free(rgb_array);

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}