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problem with loop

 
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  #1
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???
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Re: problem with loop

 
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  #2
Aug 19th, 2007
So, you are having trouble with language constructs or logic?
Last edited by SpS; Aug 19th, 2007 at 10:49 pm.
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Re: problem with loop

 
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  #3
Aug 19th, 2007
c++ Syntax (Toggle Plain Text) 
  1. #include <iostream.h>
  2. #include <conio.h>
  3.  
  4. main()
  5. {
  6. 	clrscr();
  7. 	int e,n,x;
  8. 	e=1;
  9. 	  cout<<"n: ";
  10. 	  cin>>n;
  11.  
  12. 	  do
  13. 	      {
  14. 	       e=e%2;
  15. 	       cout<<"\nn: "<<e;
  16.  
  17. 	      }  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
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Re: problem with loop

 
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  #4
Aug 20th, 2007
The statement
C++ Syntax (Toggle Plain Text) 
  1. 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
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Re: problem with loop

 
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  #5
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
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Re: problem with loop

 
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  #6
Aug 20th, 2007
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Originally Posted by hoceandress View Post
#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
c++ Syntax (Toggle Plain Text) 
  1. #include <iostream>
  2. using namespace std;
  3.  
  4. int main()
  5. {
  6.  
  7.     int sum = 0,num;
  8.     cout<<"Enter the number: ";
  9.     cin>>num;
  10.  
  11.     do
  12.     {
  13.         if(!(num&1))
  14.         sum += num;
  15.     }
  16.     while (--num);
  17.     cout<<"sum of even numbers:"<<sum;
  18. }
Last edited by SpS; Aug 20th, 2007 at 2:17 am.
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Re: problem with loop

 
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  #7
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:
C++ Syntax (Toggle Plain Text) 
  1. #include <iostream>
  2. using namespace std;
  3. int main(){
  4.   int sum = 0, n = 0;
  5.  
  6.   cout << "Enter n: ";
  7.   cin >> n;
  8.  
  9.   for(int e = 2; e <= n; e+=2)
  10.     sum += e;
  11.  
  12.   cout << "Sum of even numbers from 2 to " << n << " is " << sum << endl;
  13.  
  14.   return 0;
  15.   }
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Re: problem with loop

 
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  #8
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:
c++ Syntax (Toggle Plain Text) 
  1. int e;
  2. for (e=2; e<=n; e+=2)
Last edited by darkagn; Aug 20th, 2007 at 3:02 am.
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Re: problem with loop

 
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  #9
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...
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Re: problem with loop

 
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  #10
Aug 20th, 2007
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Originally Posted by darkagn View Post
Minor point: don't forget that in C++ you must initialise your variable outside the for loop:
c++ Syntax (Toggle Plain Text) 
  1. int e;
  2. 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.
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