Need help with pset 4 resize.c

Question

I'm stuck at resize.c its not working. Code seems fine to me but it doesn't output expected image. Please help me ..

/**
 * copy.c
 *
 * Computer Science 50
 * Problem Set 4
 *
 * Copies a BMP piece by piece, just because.
 */

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

#include "bmp.h"

int main(int argc, char* argv[])
{
    // ensure proper usage
    if (argc != 4)
    {
        printf("3 Command line arguments expected\n");
        return 1;
    }

    // remember filenames
    int factor = atoi(argv[1]); //string to int
    char* infile = argv[2];
    char* outfile = argv[3];

     // ensure n is is a positive int less than or equal to 100
    if(factor < 1 || factor > 100)
    {
        printf("Scale must be a positive int less than or equal to 100\n");
        return 1;
    }

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

    // open output file
    FILE* outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        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;
    }

    // create variables for old height and width
    int oldwidth = bi.biWidth;
    int oldheight = bi.biHeight;

    // create variables for new height and width
    int newwidth = bi.biWidth * factor;
    int newheight = bi.biHeight * factor;

    // determine padding
    int oldpadding = (4 - (bi.biWidth * sizeof(RGBTRIPLE) % 4)) % 4;
    int newpadding = (4 - (newwidth * sizeof(RGBTRIPLE)) % 4) % 4;

    // update file size
    bf.bfSize = bf.bfSize * factor;

    // update image size
    bi.biSizeImage = abs(newheight) * ((newwidth - oldpadding) * sizeof(RGBTRIPLE) + newpadding);

    // update height and width
    bi.biWidth = newwidth;
    bi.biHeight = newheight;

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

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

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

    // iterate over infile's scanlines
    for (int i = 0; i < oldheight; i++)
    {
        //iterate factor no. of times
        for (int p = 0; p < factor; p++)
        {
            //move back cursor
            fseek(inptr, 54 + ((oldwidth + oldpadding) * i) , SEEK_SET);

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

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

                for (int z  = 0; z < factor; z++)
                {
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                }
            }

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

            // add new padding
            for (int k = 0; k < newpadding; k++)
            {
                fputc(0x00, outptr);
            }
        }
    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // that's all folks
    return 0;
}

Answer 1

One suggestion is to consider that bf.bfSize and bi.biSizeImage are will not always change by "factor" as the padding on each scan line may change.