c3-3 test of optimized buffersize

#include "apue.h"

#define BUFFSIZE 4096

int main(void )
{
    int n;
    char buf[BUFFSIZE];

    while( (n = read(STDIN_FILENO,buf,BUFFSIZE))  > 0)
        if(write(STDOUT_FILENO,buf,n) !=n )
            err_sys("write error");
    if (n < 0)
        err_sys("read error");
    exit(0);
}