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So I thought I finished but the image only half way is written. Not sure what I did wrong but the image scales but only the top half. I tried both ways I could think of for the loop but decided using i%factor was best.

// Copies a BMP file

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

// remember factor
int factor = atoi(argv[1]);
// remember filenames
char *infile = argv[2];
char *outfile = argv[3];
if(factor < 1 || factor > 100)
{
    printf("Please try again");
}
// open input file
FILE *inptr = fopen(infile, "r");
if (inptr == NULL)
{
    fprintf(stderr, "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;
}

// Sets new file headers equal to old ones
BITMAPFILEHEADER newbf = bf;
BITMAPINFOHEADER newbi = bi;
// Updates width and height
newbi.biWidth *= factor;
newbi.biHeight *= factor;
// Deals with padding; basically just took the old one and changed width to the new one
int newPadding = (4 - (newbi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
// Deals with size of image
newbi.biSizeImage = (newbi.biWidth * sizeof(RGBTRIPLE)+newPadding)*abs(newbi.biHeight);
newbf.bfSize = newbi.biSizeImage + 54;





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

// write outfile's BITMAPINFOHEADER
fwrite(&newbi, 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, biHeight = abs(bi.biHeight); i < biHeight; i++)
{
    //for(int q = 0; q < factor; q++)
    //{
        // fscan is nessesary because it resets the scanner to the correct position; basically prints each line factor times
        // iterate over pixels in scanline
        // sets the scanner back a line
        if(i%factor!=0)
        {
            fseek(inptr,-(padding + bi.biWidth * sizeof(RGBTRIPLE)),SEEK_CUR);
        }
        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
            // How to do this? maybe use an %?

            // Scales horizontally by printing each picture a factor times.
            for(int x = 0; x < factor; x++)
            {
                fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            }

        }

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

        // then add it back (to demonstrate how)
        // OOPS originally forgot to change padding to new.
        for (int k = 0; k < newPadding; k++)
        {
            fputc(0x00, outptr);
        }

//}
}

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;

}

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The way you do it, your outer loop would have to go over all the output lines, not input lines. So newbi instead of bi on that loop.

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