(apologies for the weird formatting. I copied directly from CS50 IDE and it came out like this.)

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

#include "bmp.h"

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

// remember filenames
//atof converts string to double. Reminder.
float f = atof(argv[1]);

//Need to add the if statement that limits f to between 0.0 and 100

char *infile = argv[2];
char *outfile = argv[3];

// 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
//Creates two structs of type BITMAPFILEHEADER, one called bf for the original file, one called bf_new for the new file
BITMAPFILEHEADER bf;
BITMAPFILEHEADER bf_new;
//Reads the input file and stores the data in the struct bf
fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);

//Assigns the values of bf to bf_new
bf_new = bf;

// read infile's BITMAPINFOHEADER
//Creates two structs of type BITMAPINFOHEADER, one called bi for the original file, one called bi_new for the new file
BITMAPINFOHEADER bi;
BITMAPINFOHEADER bi_new;
//Reads the input file and stores the data in the struct bi
fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr);

//Assigns the values of bi to bi_new
bi_new = bi;

// 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;
}


//Multiplies the width of the input file by the value of f and stores in struct bi_new
bi_new.biWidth = bi.biWidth * f;
//Multiplies the height of the input file by the value of f  and stores in struct bi_new
bi_new.biHeight = bi.biHeight * f;

// determine padding for scanlines. Both old and new files
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
int padding_new = (4 - (bi_new.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

//Sets the total image size, including pixels and padding
bi_new.biSizeImage = ((sizeof(RGBTRIPLE) * bi_new.biWidth) + padding_new) * abs(bi_new.biHeight);

//Sets the total image size in bytes. Includes pixels, padding and headers
bf_new.bfSize = bi_new.biSizeImage + 54;

// write outfile's BITMAPFILEHEADER using new data
fwrite(&bf_new, sizeof(BITMAPFILEHEADER), 1, outptr);

// write outfile's BITMAPINFOHEADER using new data
fwrite(&bi_new, sizeof(BITMAPINFOHEADER), 1, outptr);


// iterate over infile's scanlines
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
{

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

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

        //Writes the RGB triple value to the output file n times. Horizontal resize
        for (int k = 0; k < f; k++)
        {
            // write RGB triple to outfile
            fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
        }

    }

    // Add new padding
    for (int m = 0; m < padding_new; m++)
    {
        fputc(0x00, outptr);
    }

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

    // set pointer to beginning of input file scanline
    fseek(inptr, 54 + (bi.biWidth * 3 + padding_new) * i, SEEK_SET);

}

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;

}

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

#include "bmp.h"

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

    // remember filenames
    //atof converts string to double. Reminder.
    float f = atof(argv[1]);

    //Need to add the if statement that limits f to between 0.0 and 100

    char *infile = argv[2];
    char *outfile = argv[3];

    // 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
    //Creates two structs of type BITMAPFILEHEADER, one called bf for the original file, one called bf_new for the new file
    BITMAPFILEHEADER bf;
    BITMAPFILEHEADER bf_new;
    //Reads the input file and stores the data in the struct bf
    fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);

    //Assigns the values of bf to bf_new
    bf_new = bf;

    // read infile's BITMAPINFOHEADER
    //Creates two structs of type BITMAPINFOHEADER, one called bi for the original file, one called bi_new for the new file
    BITMAPINFOHEADER bi;
    BITMAPINFOHEADER bi_new;
    //Reads the input file and stores the data in the struct bi
    fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr);

    //Assigns the values of bi to bi_new
    bi_new = bi;

    // 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;
    }


    //Multiplies the width of the input file by the value of f and stores in struct bi_new
    bi_new.biWidth = bi.biWidth * f;
    //Multiplies the height of the input file by the value of f  and stores in struct bi_new
    bi_new.biHeight = bi.biHeight * f;

    // determine padding for scanlines. Both old and new files
    int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    int padding_new = (4 - (bi_new.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    //Sets the total image size, including pixels and padding
    bi_new.biSizeImage = ((sizeof(RGBTRIPLE) * bi_new.biWidth) + padding_new) * abs(bi_new.biHeight);

    //Sets the total image size in bytes. Includes pixels, padding and headers
    bf_new.bfSize = bi_new.biSizeImage + 54;

    // write outfile's BITMAPFILEHEADER using new data
    fwrite(&bf_new, sizeof(BITMAPFILEHEADER), 1, outptr);

    // write outfile's BITMAPINFOHEADER using new data
    fwrite(&bi_new, sizeof(BITMAPINFOHEADER), 1, outptr);


    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {

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

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

            //Writes the RGB triple value to the output file n times. Horizontal resize
            for (int k = 0; k < f; k++)
            {
                // write RGB triple to outfile
                fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            }

        }

        // Add new padding
        for (int m = 0; m < padding_new; m++)
        {
            fputc(0x00, outptr);
        }

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

        // set pointer to beginning of input file scanline
        fseek(inptr, 54 + (bi.biWidth * 3 + padding_new) * i, SEEK_SET);

    }

        // close infile
        fclose(inptr);

        // close outfile
        fclose(outptr);

        // success
        return 0;

}