Print Upside Down

From one of the forums i was reading i got the idea of creating this program.Inputs some line of text and prints them as it was traversed from up to down when arranged in a row-column like structure.

Sample Input:-

ABCD
BMNF

Output:-

ABBMCNDF

#include <stdio.h>
#include <string.h>
#define BYTES 512

void pud(char *p,int o)
{
    if(!*p)return;
    int len=strlen(p);
    if(len>o)
        putchar(*(p+o));
    while(*p++);        /*points to first character of the next line*/
    pud(p,o);
}

int main()
{
    char str[BYTES];
    int i,max=0x0,j=0x0,t,size;
    
    size=fread(str,1,BYTES - 0x1,stdin);
    str[size]='\x00';
    
    for(i=0x0;i<size;i++){
         if(str[i]=='\n'){
             str[i]='\x00'; /*to make it usable by strlen*/
             t=strlen(&str[j]);
             if(t>max)
                 max=t;
             j=i + 0x1;
             }
    }

    for(i=0x0;i<max;i++)
        pud(str,i);
        
    return 0x0;
}