Today I was submitting a solution to a problem related to STRUCTURES ... I received a "COMPILATION ERROR" Although the code was working properly on my editor (Code Blocks). The message I received after submitting was "Can't compile file: reference to '(name of the structure)' is ambiguous."

I was confused because this is my first code using structures and I don't know what is the problem . What might matter is that I'm using an array of structures with size of (4*e6), and in the global scope. If anyone can explain what is the problem I will be so grateful. Thank you in advance .....

PS: After searching I found that my problem can be solved by using (using std :: cin ...::cout ....) instead of (using namespace std;) but still don't know what is the difference.

NOT

I have set a goal of becoming expert by the end of 2022, Can you give me advise and plans that I should stick to.

Thanks in advance ... Wish you all the best and a happy new year.