My code comes up with all green smiles on check50, but valgrind shows memory leaks. I don't think I fully understand pointers or malloc, yet.

Here's my code:

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

#include "bmp.h"

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

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

int scan = 0;
int cycle = 0;
int curser = 0;
int seek = 0;

if(size < 1 || size > 100)
{
    printf("Could not resize. Error: 0 < Size > 101\n");
    return 5;
}

// 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;
BITMAPFILEHEADER nbf;
fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);

// read infile's BITMAPINFOHEADER
BITMAPINFOHEADER bi;
BITMAPINFOHEADER nbi;    
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;
}

//Resize Header Values for the new file
nbf = bf;
nbi = bi;
nbf.bfSize -= nbi.biSizeImage;
nbi.biWidth *= size;
nbi.biHeight *= size;

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

nbi.biSizeImage = ((nbi.biWidth) * sizeof(RGBTRIPLE) + npadding) * abs(nbi.biHeight);
nbf.bfSize += nbi.biSizeImage;


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

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

// iterate over infile's scanlines
for (int i = 0, nbiHeight = abs(nbi.biHeight); i < nbiHeight; i++)
{
    if(cycle % size != 0)
        {
            fseek(inptr, -seek, SEEK_CUR);
        }

    // 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);
            
                for(scan = 0; scan < size; scan++)
                {
                    // write RGB triple to outfile
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                    curser = ftell (inptr);
                } 
        }
    
    // skip over padding, if any
    fseek(inptr, padding, SEEK_CUR);

    // then add it back (to demonstrate how)
    for (int k = 0; k < npadding; k++)
    {
        fputc(0x00, outptr);
    }cycle++;
}

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// that's all folks
return 0;
}

Here's valgrind:

~/workspace/pset4/bmp/ $ valgrind resize
==96876== Memcheck, a memory error detector
==96876== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==96876== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==96876== Command: resize
==96876== 
COLUMNS=133;
LINES=10;
export COLUMNS LINES;
==96876== 
==96876== HEAP SUMMARY:
==96876==     in use at exit: 605 bytes in 4 blocks
==96876==   total heap usage: 4 allocs, 0 frees, 605 bytes allocated
==96876== 
==96876== 10 bytes in 1 blocks are definitely lost in loss record 1 of 4
==96876==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==96876==    by 0x401D3E: ??? (in /usr/bin/resize)
==96876==    by 0x400EA4: ??? (in /usr/bin/resize)
==96876==    by 0x4E58EC4: (below main) (libc-start.c:287)
==96876== 
==96876== 11 bytes in 1 blocks are definitely lost in loss record 2 of 4
==96876==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==96876==    by 0x401D3E: ??? (in /usr/bin/resize)
==96876==    by 0x400F9C: ??? (in /usr/bin/resize)
==96876==    by 0x4E58EC4: (below main) (libc-start.c:287)
==96876== 
==96876== 16 bytes in 1 blocks are definitely lost in loss record 3 of 4
==96876==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==96876==    by 0x401D3E: ??? (in /usr/bin/resize)
==96876==    by 0x400EDC: ??? (in /usr/bin/resize)
==96876==    by 0x4E58EC4: (below main) (libc-start.c:287)
==96876== 
==96876== LEAK SUMMARY:
==96876==    definitely lost: 37 bytes in 3 blocks
==96876==    indirectly lost: 0 bytes in 0 blocks
==96876==      possibly lost: 0 bytes in 0 blocks
==96876==    still reachable: 568 bytes in 1 blocks
==96876==         suppressed: 0 bytes in 0 blocks
==96876== Reachable blocks (those to which a pointer was found) are not shown.
==96876== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==96876== 
==96876== For counts of detected and suppressed errors, rerun with: -v
==96876== ERROR SUMMARY: 3 errors from 3 contexts (suppressed: 0 from 0)