In Mma you dislike to use Do[], For[] or While[] for such an excercise because there is Table[]:
In[31]:= N[8 (Plus @@ Table[10^(-2 o), {o, 0, 7}])/100, 32]
Out[31]= 0.080808080808080800000000000000000
If you are forced to use For[], you write
In[33]:= Block[{x = 0}, For[o = 1, o < 9, o++, x += 8 10^(-2 o)]; N[x, 32]]
Out[33]= 0.080808080808080800000000000000000
If you are forced to use Do[], you write
In[37]:= Block[{x = 0}, Do[x += 8 10^(-2 o), {o, 1, 8}]; N[x, 32]]
Out[37]= 0.080808080808080800000000000000000
If you are forced to use While[¨], you write
In[41]:= N[Block[{x = 0, o = 1}, While[o < 9, x += 8 10^(-2 o); o++]; x], 32]
Out[41]= 0.080808080808080800000000000000000
If you are forced to use the Do[] with a condition on the iteration variable you compute that condition
In[49]:= N[Block[{x = 0}, Do[x += 8 10^(-2 o), {o, 1, Ceiling[Log[10, 8/0.0001]]}]; x], 32]
Out[49]= 0.080808080800000000000000000000000
Regards
Udo.
