recursion

[jw]

Hi all,i have a recursive function and in main for ex it takes 5 as a
parameter,n'll equal to 5 and than decrease.At the end it ll be 1 and
why doesnt the result equal to 1 because of this=>
if(n==1)
return 1


-----
int sum(int n){
if(n==1)
return 1;
else
return sum(n-1)+n;
}
void main(){
cout<<sum(5);
}

[Josh Mcfarlane]

Re: recursion

jw wrote:[color=blue]
> Hi all,i have a recursive function and in main for ex it takes 5 as a
> parameter,n'll equal to 5 and than decrease.At the end it ll be 1 and
> why doesnt the result equal to 1 because of this=>
> if(n==1)
> return 1
>
>
> -----
> int sum(int n){
> if(n==1)
> return 1;
> else
> return sum(n-1)+n;
> }
> void main(){
> cout<<sum(5);
> }[/color]

So output should be
sum(5-1) + 5
5 + 4 + sum(4-1) and onward
So you should end up with
5 + 4 + 3 + 2 + 1, or 15 if my math serves me correctly.

What's the problem?

[Alf P. Steinbach]

Re: recursion

* jw:[color=blue]
> Hi all,i have a recursive function and in main for ex it takes 5 as a
> parameter,n'll equal to 5 and than decrease.[/color]

In a sense the parameter's value decreases, but don't take that too
literally.

Each call of the function has it's own parameter value.

[color=blue]
> At the end it ll be 1 and
> why doesnt the result equal to 1 because of this=>
> if(n==1)
> return 1[/color]

That specifies only the result for that call of the function.

[color=blue]
> int sum(int n){
> if(n==1)
> return 1;
> else
> return sum(n-1)+n;
> }
> void main(){[/color]

The 'main' return type must be 'int'.

See FAQ item 29.3, "Should I use void main or int main?".


[color=blue]
> cout<<sum(5);
> }[/color]

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Alf P. Steinbach]

Re: recursion

* Josh Mcfarlane:[color=blue]
> jw wrote:[color=green]
> > Hi all,i have a recursive function and in main for ex it takes 5 as a
> > parameter,n'll equal to 5 and than decrease.At the end it ll be 1 and
> > why doesnt the result equal to 1 because of this=>
> > if(n==1)
> > return 1
> >
> >
> > -----
> > int sum(int n){
> > if(n==1)
> > return 1;
> > else
> > return sum(n-1)+n;
> > }
> > void main(){
> > cout<<sum(5);
> > }[/color]
>
> So output should be
> sum(5-1) + 5
> 5 + 4 + sum(4-1) and onward
> So you should end up with
> 5 + 4 + 3 + 2 + 1, or 15 if my math serves me correctly.
>
> What's the problem?[/color]

I think the problem is you solved jw's homework problem instead of what
he literally asked for.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

[Ron Natalie]

Re: recursion

jw wrote:[color=blue]
> Hi all,i have a recursive function and in main for ex it takes 5 as a
> parameter,n'll equal to 5 and than decrease.At the end it ll be 1 and
> why doesnt the result equal to 1 because of this=>
> if(n==1)
> return 1
>
>
> -----
> int sum(int n){
> if(n==1)
> return 1;
> else
> return sum(n-1)+n;
> }
> void main(){
> cout<<sum(5);
> }
>[/color]
Main returns int by the way.

While the sun(1) is the last one CALLED, it's not the one that
returns to main, it returns to the sum(2) call.

[Cy Edmunds]

Re: recursion

"jw" <jackwht@gmail. com> wrote in message
news:1133476524 .692164.269870@ o13g2000cwo.goo glegroups.com.. .[color=blue]
> Hi all,i have a recursive function and in main for ex it takes 5 as a
> parameter,n'll equal to 5 and than decrease.At the end it ll be 1 and
> why doesnt the result equal to 1 because of this=>
> if(n==1)
> return 1
>
>
> -----
> int sum(int n){
> if(n==1)
> return 1;
> else
> return sum(n-1)+n;
> }
> void main(){
> cout<<sum(5);
> }
>[/color]

The code above is the same as:

int sum1() {
return 1;
}


int sum2() {
return sum1()+2;
}


int sum3() {
return sum2()+3;
}


int sum4() {
return sum3()+4;
}


int sum5() {
return sum4()+5;
}

int main(){ // note: the return type of main() is int, not void
cout<<sum5();
}

[Josh Mcfarlane]

Re: recursion

Alf P. Steinbach wrote:[color=blue]
> I think the problem is you solved jw's homework problem instead of what
> he literally asked for.[/color]

Whoops, I figured he was wondering why it didn't output 1, and figured
showing him step by step what it was doing would be easiest way to
understand.

Josh McFarlane

[jw]

Re: recursion


Josh Mcfarlane wrote:[color=blue]
> Alf P. Steinbach wrote:[color=green]
> > I think the problem is you solved jw's homework problem instead of what
> > he literally asked for.[/color]
>
> Whoops, I figured he was wondering why it didn't output 1, and figured
> showing him step by step what it was doing would be easiest way to
> understand.
>
> Josh McFarlane[/color]

it is not my homework i saw it in a book and wondered,and if it had
been a homework i wouldnt have asked it to the group because the best
way to learn is doing homeworks without any help.thanks to people who
helped me..