../t26charge.c:20: warning: return type defaults to 'int'

ISR(TIMER0_OVF0_vect)
{
    ++time_count;//18310 - 10 min
    if(time_count==18310)
        {
            time_count=0;
            ++time;
            if(time==max_time)
                {
                    status |= (1<<7);
                }
        }
}

../t26charge.c:20: warning: type of '__vector_6' defaults to 'int'
../t26charge.c:31: warning: control reaches end of non-void function

#include <avr/interrupt.h>

return 0;