Why are these different?

Question

int x [] = {1,2,3,4};
for (int i=3; i>=0; i--)
{
cout << x [i] << endl;
}
Output: 4, 3, 2, 1

int x [] = { 10,20,30,40,50,69}
for (int i=0; i <6; i=i+2)
{
cout << x [i] << endl;
}
Output: 10, 30, 50

My question is, what is this saying/what's the difference between the two for this part:

for (int i=3; i>=0; i--) and for (int i=0; i <6; i=i+2)

Answer 1

Well if you have an array lets say int x = {1,2,3,4,5} the first for, which is (i=4;i>=0;i--) will scan all the array from the last int to the first (5,4,3,2,1) the second for (i=0;i <6; i=i+2) will scan only the 1st the 3rd and the 5th (1,3,5)..

Answer 2

well its about for syntax.. inside the for you declare the (initial; condition; increment) so in the for(i=0;i<6;i=i+2) your i becomes first 0 then i+2 which is 0+2=2, afterwards 2+2=4 and afterward 4+2=6 which makes the condition i < 6 false and cause of that the for loop stops.. so i in the for takes the values 0,2,4 which those index in the array got the values 1,3,5..

Answer 3

Still not understanding... :\
Why is this scanning the 1st the 3rd and the 5th?

for (i=0;i <6; i=i+2) will scan only the 1st the 3rd and the 5th (1,3,5)

Answer 4

declaration loop for (A; B; C)
A is the initial value, example i=0
B is the limit which break loop for, example i < 6
C is the step of increase or decrease of the value, example i=i+2

for (i=0;i <6;i=i+2) result
i=0 after i=0+2, i =2 < 6 continue
i=2 after i=2+2, i =4 < 6 continue
i=4 after i=4+2, i =6 not < 6 break

Answer 5

you're welcome

Answer 6

That's a little bit more helpful, thank you!
But why is it 1,3,5? The array index for loop we are discussing is {5,4,3,2,1}. Shouldn't it be 5,3,1?

Answer 7

Thank you, MBZH31! That's very clear!