I understand about prefix and postfix, but what is function num++ below this?

Question

#include <iostream>
using namespace std;

int main()
{
int num = 1;
while (num < 6) {
cout << "Number: " << num << endl;
num++;
}

return 0;
}

Answer 1

num is a variable you declared in the first line inside main().
Inside the while loop you are just incrementing that variable so it is updated every time before going for a condition check inside the while().

Sorry but it looks like you didn't understand prefix and postfix yet.
Also num is not a function but a variable.
Kindly consider revisiting the basics of the language.