I don't get it

Question

So, I was in playground mode the other day and I was trying this code:
int num = 1;
for (x = 1; x < 6; x+= 3)
{
num*= x;
}
Console.WriteLine(x)
the output was 4. Normal, right? So, I decided to sum 2 instead of 3. This code was like this:
int num = 1;
for (x = 1; x < 6; x+= 2)
{
num*= x;
}
Console.WriteLine(x)
I thought "Oh, the output will be 5" but NO. The output is 15!
My only question is why? Why is it 15? I don't get it, please help.

Answer 1

i am sure that you mean console.writeline(num)
_______________________________
for first code :
______________
*) x=1 so x<6 then num=num*x=1*1
*)x=x+3=1+3=4
*)x=4 so x<6 then num=num*x=1*4=4
*)x=x+3=4+3=7
*)x not <6 then we go out of loop
*)writing x give 7 but writing num will give 4
___________________________________________
for second code:
_________________
*) x=1 so x<6 then num=num*x=1*1
*)x=x+2=1+2=3
*)x=3 so x<6 then num=num*x=1*3=3
*)x=x+2=3+2=5
*)x=5 so x<6 then num=num*x=3*5=15
*)x=x+2=5+2=7
*)x not <6 then we go out of loop
*)writing x give 7 but writing num will give 15
___________________________________________
when you say a*=b you mean a after this operation=the value of a before this operation *the value of b
and same thing for += but with +
___________________________________________

Answer 2

Yeah, it was WriteLine(num) sorry and thank you! Now I get it