can I use void main() instead of using namespace std

Answer 1

no way
if u don't want to right using namespace
then u mention .h with header file
like <iostream.h>

Answer 2

it's totally difirent , the void is just a data type of the function main and it return to nothing(like return 0 in int main) but you do not need to write the word return in void main. you can use std::cout/cin instead of using namespace std

Answer 3

hu, it's bad practice to use void man instead of int main

Answer 4

using namespace std; allows you to not need std:: in front of things like cout and endl, etc.

Answer 5

No.
void main (): is the function where the compilation and execution starts
namespace std: was advanced version to use '.h'.