DaniWeb Forum Index > Software Development > C++

problem with loop

Please support our C++ advertiser: Intel Parallel Studio Home

•

Join Date: Aug 2007

Posts: 12

Reputation: hoceandress is an unknown quantity at this point

Solved Threads: 1

hoceandress hoceandress is offline

Offline

Newbie Poster

problem with loop

Aug 19th, 2007

will calculate and display the sum of all even even numbers from 2 to n, where n is a positive number inputted by the user..what will i do and what is the expression of that???

•

Join Date: Aug 2005

Posts: 598

Reputation: SpS is on a distinguished road

Solved Threads: 32

SpS

Offline

Posting Pro

Re: problem with loop

Aug 19th, 2007

So, you are having trouble with language constructs or logic?

Last edited by SpS; Aug 19th, 2007 at 10:49 pm.

•

Join Date: Aug 2007

Posts: 12

Reputation: hoceandress is an unknown quantity at this point

Solved Threads: 1

hoceandress hoceandress is offline

Offline

Newbie Poster

Re: problem with loop

Aug 19th, 2007

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
#include <iostream.h>
#include <conio.h>
 
main()
{
	clrscr();
	int e,n,x;
	e=1;
	  cout<<"n: ";
	  cin>>n;
 
	  do
	      {
	       e=e%2;
	       cout<<"\nn: "<<e;
 
	      }  while ((e<=n) && (e++));
#include <iostream.h>
#include <conio.h>

main()
{
	clrscr();
	int e,n,x;
	e=1;
	  cout<<"n: ";
	  cin>>n;

	  do
	      {
	       e=e%2;
	       cout<<"\nn: "<<e;

	      }  while ((e<=n) && (e++));

this my problem i can't fix it!! where n is a positive number inputted by the user. display the sum of all even numbers form 2 to n??using loop.

Last edited by stymiee; Aug 20th, 2007 at 11:33 am. Reason: added code tags

•

Join Date: Aug 2007

Posts: 801

Reputation: darkagn has a spectacular aura about

Solved Threads: 110

darkagn

Offline

Practically a Posting Shark

Re: problem with loop

Aug 20th, 2007

The statement

Help with Code Tags

C++ Syntax (Toggle Plain Text)

e=e%2;

will result in e being equal to the remainder of the division of e by 2. In other words, if e is even, e will become 0, if e is odd, e will become 1, and e will not change after that no matter how many times you loop.
To display the sum of all even numbers, you will need TWO variables, one for the sum and one for the even numbers. You should loop according to the even numbers until you get to n, add add them up using the sum.
Have a go and let us know if you need more help.

Cheers
darkagn

•

Join Date: Aug 2007

Posts: 4

Reputation: jsap is an unknown quantity at this point

Solved Threads: 1

jsap

Offline

Newbie Poster

Re: problem with loop

Aug 20th, 2007

you might not want to use a do while loop in case the user enters a value less than 1.

also e++ doesn't need to be a part of the conditional check

and you need to check if the value of e%2 is a multiple of 2 before printing to the screen

•

Join Date: Aug 2005

Posts: 598

Reputation: SpS is on a distinguished road

Solved Threads: 32

SpS

Offline

Posting Pro

Re: problem with loop

Aug 20th, 2007

•

Originally Posted by hoceandress

#include <iostream.h>
#include <conio.h>

main()
{
clrscr();
int e,n,x;
e=1;
cout<<"n: ";
cin>>n;

do
{
e=e%2;
cout<<"\nn: "<<e;

} while ((e<=n) && (e++));

this my problem i can't fix it!! where n is a positive number inputted by the user. display the sum of all even numbers form 2 to n??using loop.

There are plenty of problems in your code
1) You are using non-standard headers(iostraem.h,conio.h). You should be sticking to standard headers. You only require <iostream> in your code.
2)Implicit int in main is wrong. main always returns int.
3)clrscr() is again non-standard function. Better not use it.
4) Use more descriptive variable names.
You should be doing something like this

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
#include <iostream>
using namespace std;
 
int main()
{
 
    int sum = 0,num;
    cout<<"Enter the number: ";
    cin>>num;
 
    do
    {
        if(!(num&1))
        sum += num;
    }
    while (--num);
    cout<<"sum of even numbers:"<<sum;
}
#include <iostream>
using namespace std;

int main()
{

    int sum = 0,num;
    cout<<"Enter the number: ";
    cin>>num;

    do
    {
        if(!(num&1))
        sum += num;
    }
    while (--num);
    cout<<"sum of even numbers:"<<sum;
}

Last edited by SpS; Aug 20th, 2007 at 2:17 am.

•

Join Date: Jun 2007

Posts: 275

Reputation: dougy83 is on a distinguished road

Solved Threads: 45

dougy83

Offline

Posting Whiz in Training

Re: problem with loop

Aug 20th, 2007

Sequential even numbers are 2 apart, so what's wrong with going from 2 to n in steps of 2?

For example:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
using namespace std;
int main(){
  int sum = 0, n = 0;
 
  cout << "Enter n: ";
  cin >> n;
 
  for(int e = 2; e <= n; e+=2)
    sum += e;
 
  cout << "Sum of even numbers from 2 to " << n << " is " << sum << endl;
 
  return 0;
  }
#include <iostream>
using namespace std;
int main(){
  int sum = 0, n = 0;
  
  cout << "Enter n: ";
  cin >> n;
  
  for(int e = 2; e <= n; e+=2)
    sum += e;
    
  cout << "Sum of even numbers from 2 to " << n << " is " << sum << endl;
  
  return 0;
  }

•

Join Date: Aug 2007

Posts: 801

Reputation: darkagn has a spectacular aura about

Solved Threads: 110

darkagn

Offline

Practically a Posting Shark

Re: problem with loop

Aug 20th, 2007

Yes dougy83 that is what i was getting at, but I didn't want to give away the answer.

Minor point: don't forget that in C++ you must initialise your variable outside the for loop:

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
int e;
for (e=2; e<=n; e+=2)
int e;
for (e=2; e<=n; e+=2)

Last edited by darkagn; Aug 20th, 2007 at 3:02 am.

•

Join Date: Aug 2007

Posts: 12

Reputation: hoceandress is an unknown quantity at this point

Solved Threads: 1

hoceandress hoceandress is offline

Offline

Newbie Poster

Re: problem with loop

Aug 20th, 2007

thankxz man!!!thanks for suggestion and the code, it really helps me a lot..

i didn't think the other expression..that's a mess of me!! thanks also to jsap and darkagn...

•

Join Date: Aug 2005

Posts: 598

Reputation: SpS is on a distinguished road

Solved Threads: 32

SpS

Offline

Posting Pro

Re: problem with loop

#10

Aug 20th, 2007

•

Originally Posted by darkagn

Minor point: don't forget that in C++ you must initialise your variable outside the for loop:
Help with Code Tags

c++ Syntax (Toggle Plain Text)
int e;
for (e=2; e<=n; e+=2)
int e; for (e=2; e<=n; e+=2)

That's incorrect. It was only required in C89/90. C++ never had such requirement. Even C99 removes this restriction.