Question

I’m wondering where to put using namespace std;. I saw a code with the using namespace std; in the int main(){} but I was putting it after #include <iostream>. Where should I put it and does it make any difference where I put it?

Answer 1

It makes a huge difference where you put it.

If you put it inside a function, then it only applies in that function.

If you put it outside a function in global scope then it applies to everything after that point.

If you put it outside a function in global scope in a header file then it will even apply to ever file that includes that header.

Generally, it’s very bad practice to use it at global scope in a header, and semi bad practice to use it in global scope at all since in Unity builds, the distinction between headers and source files is blurred.

You would be best to just use it in the functions that you need it, or even not use it at all and just prefix standard library functions/classes with std::.