circular buffer resets memory?

circular buffer resets memory?

When this cycles back around dd[0] is set to 0 as apposed to 256.1 ?? It
seems like 'dd' memory is resetting with 'aa' back to 0.
unsigned char aa = 0;
double *dd = new double[256];
//circular buffer
dd[aa] = 0.1;
for(int i = 0; i < 600; i++){
qstr += QString::number(aa,'d',0) + " " +
QString::number(dd[aa],'f',1) + " ";
aa++;//onces 'aa' reaches 255, the next increment resets back to 0 for
'aa'
dd[aa] = dd[aa - 1] + 1;
}