performance - C++ Efficency of variable declaration

I have a curiosity.

I would like to know if it is more efficient this code

int a(0);
for(int i=0;i!=10;++i){
    a=0;
    for(int j=0;j!=10;++j){
        // perform some operations on a
    }
} 

or this code

for(int i=0;i!=10;++i){
    int a(0);
    for(int j=0;j!=10;++j){
        // perform some operations on a
    }
} 

or it is exactly the some in term of performance. I understand that the answer may depend on the compiler and its inner optimization technique but I am curios to understand if there is any difference.

Thank you,
Marco.

Answer

In any modern C++ compiler there's no difference what-so-ever.