while loop does not end

[snekus001]

Hi. Why does my while loop never end? Even if I enter 0 , it still lets me enter. The program should end, when I at least type one time 0 (either in "food", or "people").

 #include <iostream>
#include <iomanip>
#include <cmath>

using namespace std;
   int main ()
{
    int food, people, days=0 ;
   while ((food!=0) || (people!=0))
   {
       cin>>food>>people;
days++;
   }
cout<<days;
return 0;
}

[Peter87]

The loop will stop if you enter 0 for both food and people.

You need to initialize food and people before the loop (or use a do-while loop) to prevent that they are used before being initialized.

[snekus001]

Thanks. I don't really understand how to initialize ? Can you please show me? Sorry, i am new to programing and don't have any examples. Searched the web, but could not find an easy to understand example.

[Peter87]

Initialization just means you give a variable a starting value (like you do with days).

If you don't do this your program might not work properly. When I tested your program it never even entered the loop because of this.

[snekus001]

Maybe i should use " while ((food>0) || (people>0)) " ?

[Handy Andy]

Hello snekus001,

Try initializing your variables before you use them. As your program is written "food" and "people" have unknown values and no guarantee that the while condition will work. When I tried compiling your original code I received errors for uninitialized variables.

You could also try: while ((food!=0) && (people!=0)). I have seen times where "&&" has to be used with two "!=" to work correctly.

Remember both "food" and "people" have to be zero for the while loop to fail. And the way the while is written "days" will likely be one more than you want.

Hope that helps,

Andy

[Chervil]

First, none of the variables are initialised. When reaching line 9 for the first time, what will happen - will the loop execute or will it end? There's no way to tell, since the contents of the variables are unknown (garbage).

As for the loop condition itself, it uses the logical OR operator || to combine two conditions.

Let's look at an example:

food    people    (food!=0)    (people!=0)    ((food!=0) || (people!=0))
  5       5         true         true                  true
  5       0         true         false                 true
  0       5         false        true                  true
  0       0         false        false                 false

The only case where the whole condition is false is where both of the conditions are false.

But if the operator || is changed to &&, things are different. The condition as a whole is true only when both the conditions are true. That means the condition as a whole is false when either of the conditions are false.

food    people    (food!=0)    (people!=0)    ((food!=0) && (people!=0))
  5       5         true         true                  true
  5       0         true         false                 false
  0       5         false        true                  false
  0       0         false        false                 false

The remaining question is the required outcome. Is the line days++; supposed to be executed when either/both the values are zero? Or not?

[bird1234]

food and people are not initialize so they will have a garbage value , initialize them with 1 or whatever value you want

int food=1,people=1;

[snekus001]

Thank you all :)