C++ while loop using i--

siabanie banie

14y1.9k

Hi all,

Can anyone assist me on this;

What are the values of i and j after this snippet code executed:

int i(10), j(0);
while (i- -)
j+=i;

I try to do some working steps as:

When i = 10, j = j = 0 + 10 which is 10;
When i = 9, j = j = 10 + 9 which is 19;
When i = 8, j = j = 19 + 8 which is 27;
When i = 7, j = j = 27 + 7 which is 34;
When i = 6, j = j = 34 + 6 which is 40;
When i = 5, j = j = 40 + 5 which is 45;
When i = 4, j = j = 45 + 4 which is 49;
When i = 3, j = j = 49 + 3 which is 52;
When i = 2, j = j = 52 + 2 which is 54;
When i = 1, j = j = 54 + 1 which is 55;
When i = 0, j = j = 55 + 0 which is 55 ;
When i = -1, the while loop exit.

So i = -1, j =55.

Can anyone help me what I did wrong please. Thanks

2 Replies

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Rohit14y ago
Accepted answer
Hi,

For the first run.

i will be 9 and not 10
When i = 9, j = j = 0 + 9 which is 9;
When i = 8, j = j = 9 + 8 which is 17;
When i = 7, j = j = 17 + 7 which is 24;
When i = 6, j = j = 24 + 6 which is 30;
When i = 5, j = j = 30 + 5 which is 35;
When i = 4, j = j = 35 + 4 which is 39;
When i = 3, j = j = 39 + 3 which is 42;
When i = 2, j = j = 42 + 2 which is 44;
When i = 1, j = j = 44 + 1 which is 45;
When i = 0, j = j = 45 + 0 which is 45;

exit

i=-1; j=45
Vulpes14y ago
Siabanie,

What you may be missing here is that:

'i' is first tested to see if it's zero

If it is zero then 'i' is decremented to -1 and the loop exits.

If it's not zero, then 'i' is decremented before (not after) the body of the loop is executed

So, as Rohit correctly said, 'i' will be 9 and not 10 when the loop body executes for the first time.