#include <stdio.h>
#include <stdlib.h>
#include <cs50.h>
#include "bmp.h"

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

    //atoi converts string  ex "6" to 6
    int n  = atoi(argv[1]);
    char *infile = argv[2];
    char *outfile = argv[3];

    //n  is a positive integer less than or equal to 100
    if( (n >  100) && (n <= 0) )
    {
        fprintf(stderr, "(n) must be a positive integer less than or equal to 100");
        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 4;
    }

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

    //new headerfile BITMAPINFOHEADER

    //new  bi.biWidth and new bi.biHeight
    bi.biWidth =  bi.biWidth * n;
    bi.biHeight = bi.biHeight * n;

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

    //new bi.biSizeImage
    bi.biSizeImage = ((sizeof(RGBTRIPLE) * bi.biWidth) + new_padding) * abs(bi.biHeight);



    //new headerfiles and new BITMAPINFOHEADER

    //new bf.bfsize
     bf.bfSize = bi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    // 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 createes height
        for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
        {
            // iterate over pixels in scanline creates width
            for (int j = 0; j < bi.biWidth; j++)
            {
                // temporary storage
                RGBTRIPLE triple;

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

                // write RGB triple to outfile        nth time triples
                fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            }
        }


        // skip over padding, if any
        fseek(inptr, new_padding, SEEK_CUR);
        // then add it back (to demonstrate how)
        for (int k = 0; k <  new_padding; k++)
        {
            fputc(0x00, outptr);
        }


    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}

For pset4 I don't know what is wrong. I am pretty sure my headerfiles are correct. If they wrong inform me.

I can't see anything wrong with my for loops.

Lets say I have the input of 2 Rgbtriples

input :

Rgbtriple: Rgbtriple:

  for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        // iterate over pixels in scanline creates width
        for (int j = 0; j < bi.biWidth; j++)
        {
        
        }
        

Assume n = 3.

bi.biHeight = 1 * 3 = 3. This will create a height of 3. So i = 0-2.

bi.biWidth = 2 * 3 = 6. This will create width of 6 or 6 Rgbtriples. So i = 0-2.

The reason I didn't add bi.biHeight * n and bi.biWidth * n is because they are already modified because of the new headers.

output:

Height: 0: Rgbtriple :Rgbtriple: Rgbtriple Rgbtriple: Rgbtriple 5:Rgbtriple: 0x00 0x00

Height:0: Rgbtriple Rgbtriple: Rgbtriple Rgbtriple: Rgbtriple 5:Rgbtriple: 0x00 0x00

Height: 0: Rgbtriple Rgbtriple: Rgbtriple Rgbtriple: Rgbtriple 5:Rgbtriple: 0x00 0x00

I am not really sure why fseek is needed. The padding should be correct in the code.