Collection was modified; enumeration operation may not execute.

I create method feedingtime(), all animals eat in order of birds, snake and then monkeys. If an animal does not have enough food then report that it. . . escaped.

public void Feedtime()
{

IEnumerator em = animalList.GetEnumerator();
while(em.MoveNext())
{
if(em.Current.GetType()==typeof(Bird))
{
iFoodPresent -= ((Bird)em.Current).getFoodIntake();
if (iFoodPresent>0)
{
Console.WriteLine(((Bird)em.Current).ToString()+ " have eaten, left food = "+ iFoodPresent);

}
else
{
Console.WriteLine(((Bird)em.Current).ToString()+" escaped");
animalList.Remove((Bird)em.Current);

}
}
}
em = animalList.GetEnumerator();
while(em.MoveNext())
{

if(em.Current.GetType()==typeof(Snake))
{
iFoodPresent -= ((Snake)em.Current).getFoodIntake();
if (iFoodPresent>0)
{
Console.WriteLine(((Snake)em.Current).ToString()+ " have eaten, left food = "+ iFoodPresent);

}
else
{
Console.WriteLine(((Snake)em.Current).ToString()+" escaped");
animalList.Remove((Snake)em.Current);

}
}
}
em = animalList.GetEnumerator();
while(em.MoveNext())
{
if(em.Current.GetType()==typeof(Monkey))
{
iFoodPresent -= ((Monkey)em.Current).getFoodIntake();
if (iFoodPresent>0)
{
Console.WriteLine(((Monkey)em.Current).ToString()+ " have eaten, left food = "+ iFoodPresent);
}
else
{

Console.WriteLine(((Monkey)em.Current).ToString()+" escaped");
animalList.Remove((Monkey)em.Current);

}
}
}
}

Answer this question

Collection was modified; enumeration operation may not execute.

spnz
You cannot alter a collection when using an enumerator or else the enumerator becomes invalid. If you want to remove items from a collection then use a for loop starting at the last index and moving towards the front. That way removing an item does not affect the indices of the items you are yet to visit.

Jeremy51

You can't effect a collection while enumerating. Here is the working code, but you do a very strange thing, you have a loop for every animal type that can be better:

public void Feedtime()
{
   for(int i = animalList.Count - 1; i >= 0; i++)
   {
    if(animalList[ i ].GetType()==typeof(Bird))
    {
     iFoodPresent -= ((Bird)animalList[ i ]).getFoodIntake();
     if (iFoodPresent>0)
     {
      Console.WriteLine(((Bird)animalList[ i ]).ToString()+ " have eaten, left food = "+ iFoodPresent);

     }
     else
     {
      Console.WriteLine(((Bird)animalList[ i ]).ToString()+" escaped");
      animalList.Remove((Bird)animalList[ i ]);


     }
    }
   }

   for(int i = animalList.Count - 1; i >= 0; i++)
   {
    if(animalList[ i ].GetType()==typeof(Snake))
    {
     iFoodPresent -= ((Snake)animalList[ i ]).getFoodIntake();
     if (iFoodPresent>0)
     {
      Console.WriteLine(((Snake)animalList[ i ]).ToString()+ " have eaten, left food = "+ iFoodPresent);

     }
     else
     {
      Console.WriteLine(((Snake)animalList[ i ]).ToString()+" escaped");
      animalList.Remove((Snake)animalList[ i ]);


     }
    }
   }

   for(int i = animalList.Count - 1; i >= 0; i++)
   {
    if(animalList[ i ].GetType()==typeof(Monkey))
     {
      iFoodPresent -= ((Monkey)animalList[ i ]).getFoodIntake();
      if (iFoodPresent>0)
      {
       Console.WriteLine(((Monkey)animalList[ i ]).ToString()+ " have eaten, left food = "+ iFoodPresent);
      }
      else
      {
       Console.WriteLine(((Monkey)animalList[ i ]).ToString()+" escaped");
       animalList.Remove((Monkey)animalList[ i ]);
      }
     }
    }
   }

A better loop will be (i geus the base type of you animals is Animal):

public void Feedtime()
{
    for(int i = animalList.Count - 1; i >= 0; i++)
    {
        Animal animal = (Animal)animalList[ i ];

        iFoodPresent -= animal.getFoodIntake();

        if( iFoodPresent > 0 )
        {
            Console.WriteLine( animal + " have eaten, left food = " + iFoodPresent );
        }
        else
        {
            animalList.Remove( animal );

            Console.WriteLine( animal + " escaped" );
        }
    }
}

Collection was modified; enumeration operation may not execute.

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Collection was modified; enumeration operation may not execute.

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Collection was modified; enumeration operation may not execute.

Collection was modified; enumeration operation may not execute.

spnz

Jeremy51