my code

/**
 * recover.c
 *
 * (rl777)
 * 5/25/2016
 *
 * Computer Science 50
 * Problem Set 4 - Forensics/Recover
 *
 * Recovers JPEGs from a forensic image.
 */

// https://www.codingunit.com/printf-format-specifiers-format-conversions-and-formatted-output
// https://www.branah.com/ascii-converter




// Library includes
//==================================
#include <stdio.h>
#include <string.h>
#include <cs50.h>


//Declarations
//==================================

int count;
unsigned char buf[512]; //holds the 512 bytes of a jpg block
int jpgCnt=-1;          //counts the number of jpgs detected
int blockCnt=0;         //number of blocks processed, both empty and data.
int picSize=0;          //individual image size in blocks.
bool processing=0; //used to determine if we are in the data section of the card
char name[3];
char prefix[11];
FILE* fp;          // this is the input file ptr. Pointing to card.raw


/*

long GetFileSize(const char* filename)
{
    long size;
    FILE *f;

    f = fopen(filename, "r");  //open the file
    if (f == NULL) return -1;  //
    fseek(f, 0, SEEK_END);     //point to the end of the file
    size = ftell(f);           //get the relative offset
    fclose(f);                 //close the file

    return size;               //return the size of the file
}

*/

int main(int argc, char* argv[])
{
    FILE* cardFile=fopen("card.raw","r");  //open the card file

    while (fread(buf, 512,1, cardFile) ==1)
    {
        if (  //see if this is the start of a jpg
            ((int)buf[0]==0xff) &&
            ((int)buf[1]==216) &&
            ((int)buf[2]==255) &&
            (  (int)buf[3]==224 || (int)buf[3]==225   )
            )
        {
            jpgCnt++;

            if (processing==0)   //This is the first jpg encountered. No file to close.
                {processing=1;}
            else  //This is not the first jpg encountered. Need to close open file
                {fclose(fp);
                }

            //in either case, a new jpg file is opened
            sprintf(name, "%03d", jpgCnt);   // %i or %d?
            strcat(name,".jpg");
            strcpy(prefix,"../");   //compiles ok, but checker doesn't like this.
            //strcpy(prefix,"");  //checker likes this.
            strcat(prefix,name);
            fp = fopen(prefix,"a"); //open the new jpg file
            fwrite(buf,512,1,fp);  //fp is an "append" file. Pointer will change
                                   //automatically after write.
            picSize++;
        }

        else  //Not first block of current jpg or no jpg yet
            {if (processing==1) //Append data to open jpg file
                {
                   fwrite(buf,512,1,fp);
                   picSize++;
                }
            }
    } //end of while loop, looping block-at-a-time through card file.

    // We have now exited the while loop. No more file processing.

    fclose(fp);           // close the current (the last generated) image file.
    fclose(cardFile);     // close the input file (card.raw))
    exit(0);              // is this needed?

}   /* End main */