Simple while loop question

[howellj8]

I know for while loops you type
while(argument){
do whatever
}

you have to use the brackets to enclose just like I used in my code right here.
It is a simple while loop that is a countdown.

#include <iostream>

using namespace std;

int main()
{
 int n =10;

 while(n>0){
    cout << n << ", ";
    --n;
}

cout << "Liftoff!\n";

}

My question is that when I take the brackets away from my while loop, my code will still execute but it just prints out the number "10" repeatedly. I was just wondering why it does this and why the compiler does not throw out an error when I leave off the brackets after the "while()". thanks for the help!

[2AoiNwbp]

It doesn't throw an error because it thinks you intend to do another thing...
try putting -- after the n in the condition and see what happens

regards,
Alejandro

[tath]

while (1)
    cout << "ok";

is interpreted as

while (1)
{
    cout << "ok";
}

------------------
so if you do:

 while(n>0)
    cout << n << ", ";
    --n;

it is interpreted as

 while(n>0)
{
    cout << n << ", ";
}
    --n;

[howellj8]

Oh okay.

I tried setting it up as "n--;" without the brackets and the same exact thing happened; it outputted 10 continuously. And it also worked like it is suppose to when the brackets are there. Does it not matter whether the "--" are after or before the "n"?

[Peter87]

A while loop has the form:

while ( condition ) statement

That means only the statement that directly follows is part of the loop, so if you take away the { } from your code only line 10 will be part of the loop.

A list of statements enclosed inside { } is a compound-statement, i.e. a statement that contain multiple statements and that's what you'll have to use if you want multiple statements to be part of the loop.

[2AoiNwbp]

Hi Peter,

Your explanations are so good! I still stick to my "make a simple test and see what happens..."

regards,
Alejandro

[howellj8]

@peter87

Thank you, your explanation makes a lot of sense! I am new to C++ and I don't quite have a firm grasp on the loops yet and their syntax. But I am learning. I am about to take my intro to C++ course this summer so You will probably see a lot of posts from me asking many questions! Thanks again!

and also no one had explained why "n--" and "--n" are the same thing?

[howellj8]

and thanks @that, your visual explanation combined with @peter87's explanation really helped a lot!! Thank you!

[Peter87]

The only difference between n-- and --n is the return value.

n-- returns the value of n before it was incremented.

int n = 1;
int m = n--; // m will hold the value 1 

--n returns the value of n after it has been incremented.

int n = 1;
int m = --n; // m will hold the value 0 

In your code you are not interested in the return value so it doesn't matter which one you use.

[2AoiNwbp]

and also no one had explained why "n--" and "--n" are the same thing?

It has to do with context. In any expression, like:

int n = 10;
a = --n;
b = n--;

--n will reduce n in 1 before assigning it o a, thus a will be 9
whereas
n-- will reduce n in 1 after assigning it to b, thus, b will be 9
after that, n will be 8

regards,
Alejandro

[howellj8]

ok thanks Peter and aabuezo. I understand it now. Thanks a lot again for clearing this up for me