HELP !!

[wardah]

Write an algorithm to print all even numbers in descending order and
draw the flowchart.

[code]
Put the code you need help with here.
[/c programming]

[Dy7SLyTq]

descending from what?

[SamuelAdams]

You have to ask yourself, is Zero considered to be a even number ?

if x == even
do nothing
else
subtract 1 from x

while x greater than or equal to zero
print x
subtract 2 from x

[jrfrago]

This can't be done if you want to print "all" even numbers in descending order. It is infinite, it must start from a certain even number.

[vlad from moscow]

@wardah

I think you mean that the user enters some arbitrary number and the program has to print all even numbers starting from the nearest to entered number even number descending to zero.

[metulburr]

#include <iostream>
using namespace std;


int main(){
    int start = 100;
    
    for (int i=start; i--;){
        if (i != 0){
            if (i % 2 == 0){
                cout << i << " is even" << endl;
            }
        }
    }
}

[vlad from moscow]

@metulburr

You forgot to print 100. It is also an even number.:)

[metulburr]

oh

#include <iostream>
using namespace std;


int main(){
    int start = 100;
    
    start += 1;
    for (int i=start; i--;){
        if (i != 0){
            if (i % 2 == 0){
                cout << i << " is even" << endl;
            }
        }
    }
}

[vlad from moscow]

@metulburr

In any case your code is bad.

[vlad from moscow]

#include <iostream>

int main()
{
   while ( true )
   {
      std::cout << "Enter a non-negaive number (0 - exit): ";

      unsigned int n = 0;
      std::cin >> n;

      if ( !n ) break;

      std::cout << "Even numbers between " << n << " and 0 are:\n";

      do
      {
         if ( ( n &1 ) == 0 ) std::cout << n << ' ';
      } while ( n-- != 0 );

      std::cout << std::endl;
   }
}
 

EDIT: I corrected a typo in expression n &1 == 0. Instead ( n &1 ) == 0 should be.

[metulburr]

why is it bad? aside from bringing in std namespace.

[vlad from moscow]

This loop is bad

    for (int i=start; i--;){
        if (i != 0){
            if (i % 2 == 0){
                cout << i << " is even" << endl;
            }
        }
    }

Why the check of i is inside the loop body and not in the for statement itself? It is a stupid code that only confuses the reader.

[metulburr]

ok so put the check in the loop. I still consider mine more readable than yours and not so unnecessarily complex:

#include <iostream>
using namespace std;


int main(){
    int start;
    cout << "Enter Starting number: ";
    cin >> start;
    
    for (int i=start+1; i>0; i--){
        if (i % 2 == 0){
            cout << i << " is even" << endl;
        }
    }
}

[jrfrago]

@metulburr: your code is fine and would serve the purpose of the needed function. There are several ways to implement loops and vlad from moscow just prefers usng the do-while. I would prefer using just the while.


The line (in vlad from moscow's code)

if ( !n ) break;

is unnecessary; the do-while code is enough.

not unless, entering 0 is designed to get out of the program.

Also,

the line if ( n &1 == 0 ) doesn't work, should have been if ( n%2 == 0 ).

[vlad from moscow]

@jrfrago
the line if ( n &1 == 0 ) doesn't work, should have been if ( n%2 == 0 ).

Who did say you that if ( n &1 == 0 ) doesn't work?

Simply there is a typo. Should be

if ( ( n &1 ) == 0 )

[vlad from moscow]

@metulburr

Why was start declared as int? Does your program process negative numbers correctly? The outpput of the program does not look good because every even number is followed by text "is even" in new line.
Moreover your program has a bug. If for example the user will enter number 101 you will display that number 102 is even. It is already your second attempt that you can not write the code correctly.

#include <iostream>
using namespace std;


int main(){
    int start;
    cout << "Enter Starting number: ";
    cin >> start;
    
    for (int i=start+1; i>0; i--){
        if (i % 2 == 0){
            cout << i << " is even" << endl;
        }
    }
}

[ne555]

> Does your (metulburr's) program process negative numbers correctly?
Yes, it does.
¿what about yours?


(referring to http://www.cplusplus.com/forum/beginner/106592/#msg577348 )
> Why the check of i is inside the loop body and not in the for statement itself?
It does check for `i' in the condition of the loop. The if is superfluous.

[vlad from moscow]

@ne555

¿what about yours?

It considers all numbers as non-negative. So logically it is correct.


[quote]@ne555

It does check for `i' in the condition of the loop. The if is superfluous/quote]

    for (int i=start; i--;){
        if (i != 0){

The check if (i != 0){ is outside the for statement. It is not clear why it is placed outside the for statement and executed as many times as the loop itself. This only confuses the reader. He has to understand why such strange constrauction was selected instead of a simple loop.

[jrfrago]

The program needs to print even numbers in descending order. If you would consider negative numbers, the beginning and the end must be defined as it moves to the left of the number line and it would do so indefinitely. It is not clear what wardah wants. Your codes are both correct (yes, that was a typo which I ddn't recognize immediately) as far as considering positive even numbers are concerned.