c++ - Which algorithm brings the best performance?

I have a piece of code that is really
dirty.

I want to optimize it a little bit. Does
it makes any difference when I take one of the following structures or are they
identical with the point of view to performance in c++
?

for(unsigned int i =
            1; i < entity.size(); ++i) begin
if
 if ... else
            ...
for end

for(unsigned int i = 1; i < entity.size();
            ++i) begin
if
 if ... else ...
for
            end


for(unsigned int i = 1; i < entity.size(); ++i)
            begin
if
 if ... else ...
for
            end
....

or

for(unsigned
            int i = 1; i < entity.size(); ++i) begin
if
 if ... else
            ...
if
 if ... else ...
if
 if ... else
            ...
....
for
            end

Thanks
in Advance!