resize.c new version

/**
 * resize.c
 *
 * Computer Science 50
 * Problem Set 4
 *
 * Resizes a bmp by a factor ranging from 0 to 100 inclusive.
 * I am starting with the code supplied by CS50 course called
 * copy.c
 *
 * Changes to the code of copy.c written by
 * Jon Hjerting
 * March 2016
 *
 *
 */

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

#include "bmp.h"

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

    // check n value
    int n = atoi(argv[1]);
    if (n < 1 || n > 100)
    {
        printf("n must be an integer in the range [1, 100]");
        return 5;
    }

    // remember filenames
    char* infile = argv[2];
    char* outfile = argv[3];

    // open input file
    FILE* inptr = fopen(infile, "r");
    if (inptr == NULL)
    {
        // abort if file failed to open
        printf("Could not open %s.\n", infile);
        return 2;
    }

    // open output file
    FILE* outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        // abort if opening new file failed
        fclose(inptr);
        fprintf(stderr, "Could not create %s.\n", outfile);
        return 3;
    }

    // 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 4;
    }

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

    // original width and height
    int oldWidth = bi.biWidth;
    int oldHeight = abs(bi.biHeight);

    // update width
    bi.biWidth *= n;

    // update height
    bi.biHeight *= n;

    // determine new padding for enlarged file
    int newPadding =  (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    // update biSizeImage
    bi.biSizeImage = (bi.biWidth * sizeof(RGBTRIPLE) + newPadding) * abs(bi.biHeight);

    // update bfSize
    bf.bfSize = bi.biSizeImage + bf.bfOffBits;

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

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

    // pixel counter for position in array
    int pixelNo;

    // array for storing one line of pixels
    RGBTRIPLE lineArray[bi.biWidth];
    int arraySize = sizeof(RGBTRIPLE) * bi.biWidth;

    // iterate over infile's scanlines
    for (int line = 0; line < oldHeight; line++)
    {
        // counter for inserting pixel in lineArray
        pixelNo = 0;

        // iterate over pixels in scanline
        for (int pixel = 0; pixel < oldWidth; pixel++)
        {
        // temporary storage
            RGBTRIPLE triple;

            // read RGB triple from infile
            fread(&triple, sizeof(RGBTRIPLE), 1, inptr);

            // repeat n times to enlarge width by n
            for (int repeatpixel = 0; repeatpixel < n; repeatpixel++)
            {
                // write RGB triple to lineArray
                lineArray[pixelNo] = triple;
                pixelNo++;
            }
        }

        // repeat n times writing line to file
        for (int repeatLine = 0; repeatLine < n; repeatLine++)
        {
            // write lineArray to file
            fwrite(lineArray,  arraySize, 1, outptr);

            // add padding to outfile
            for (int k = 0; k < newPadding; k++)
            {
                fputc(0x00, outptr);
            }

        }

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

    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // that's all folks
    return 0;
}