Using ++ operator leads to unexpected results - c++

Question

I do not understand why the two codes below lead to the same result. Shouldn't the latter print from 6 to 10 since n is incremented first?
Edit: I used both Visual Studio 2019 and repl.it.
#include <iostream>
using namespace std;
int main() {
int n=5;
for (n; n<10; n++)
cout << n << endl;
return 0;
}
>>> 5
6
7
8
9
#include <iostream>
using namespace std;
int main() {
int n=5;
for (n; n<10; ++n)
cout << n << endl;
return 0;
}
>>> 5
6
7
8
9

Answer 1

From https://en.cppreference.com/w/cpp/language/for
attr(optional) for ( init-statement condition(optional) ; iteration_expression(optional) ) statement
The above syntax produces code equivalent to:
{
init_statement
while ( condition ) {
statement
iteration_expression ;
}
}
Your two for loops are therefore equivalent to
{
n;
while (n < 10) {
cout << n << endl;
n++;
}
}
and
{
n;
while (n < 10) {
cout << n << endl;
++n;
}
}
In a for loop:
The first statement is executed exactly once
The conditional is checked, and if true
The body is executed
Then the iteration expression is executed
Goto (2.)
If you want your loop to start at 6, you need to explicitly tell it to start at 6.

Answer 2

There's Nothing wrong here, its just how its supposed to work
Firstly, you should know a for loop works
for loop, without loss of generality can be written as:
for(exp1; exp2; exp3)
{
//body
}
here exp1 will be executed only when entering the loop first time, then exp2 will be evaluated, if true loop will continue, otherwise not.
exp3 is evaluated only after each iteration is complete.
also the only difference between i++ and ++i, is when you assign it to something.
say i is 5, then after statement
i++;
i will be 6
which is also true for this statement:
++i;
but say i=5,
but you try something like this:
a=i++;
after this statement, a will be 5, and i will be 6.
but after this statement, with same initial condition(i = 5):
a=++i;
both a and i will be 6.

Answer 3

The only difference is this:
for (n; n<10; n++)
vs. this:
for (n; n<10; ++n)
The first and third expressions in a for statement are evaluated only for their side effects, with any result discarded. (The second is evaluated and its result used to determine whether to continue the loop.) The only difference between n++ and ++n is their results; their side effects are identical. So in this context n++ and ++n are effectively identical.
I'll also mention that the first expression n has no side effects, so it might well be omitted:
for (; n<10; n++)
Or, better yet, you could incorporate the declaration and initialization into the loop, replacing the existing declaration int n=5;:
for (int n = 5; n < 10; n++)