Property of a list<> not updating

Question

1.00/5 (1 vote)

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I have this code below:

Foood[] food = new Foood[types];
            food[0] = new Foood("protein", 2.0);
            food[1] = new Foood("vitamins", 3.0);
            food[2] = new Foood("Carbonhydrate", 4.0);

and then this

List<Foood> foods = new List<Foood>();

     foods.Add(food[0]);
     foods.Add(food[1]);
     foods.Add(food[2]);

and then this

for (int i = 0; i < days; i++)
{

    UpdateCalories(foods);

}

public void UpdateCalories(List<Foood> foodItem)
        {

            for (int i = 0; i < foodItem.Count; i++)
            {
                foodItem[i].calories = foodItem[i].calories + 1.1;
            }
        }

i want to be able to have values for different days before printing

What I have tried:

I have written and pasted the code

got this:
Day0
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

Day1
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

Day2
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

Day3
protein,5.3
vitamins,6.3
Carbonhydrate,7.3
----------------------------------------

But I want this:

Day0
protein,2.0
vitamins,3.0
Carbonhydrate,4.0

Day1
protein,3.1
vitamins,4.1
Carbonhydrate,5.1

Day2
protein,4.2
vitamins,5.2
Carbonhydrate,6.2

Day3
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

-----------------

I still want to have access to the values of the previous days not just the last day.

this is my output code
----------------------------

C#

using (StreamWriter sw = new StreamWriter(@"U:\Food\food.txt"))
{
	sw.WriteLine("Day" + "{0}", 0);
	for (int ii = 0; ii < types; ii++)
	{
		sw.WriteLine("{0},{1}", food[ii].Type, food[ii].Calories);
	}
	sw.WriteLine("");
	for (int i = 0; i < days; i++)
	{
		{
			sw.WriteLine("Day" + "{0}", i + 1);
			for (int ii = 0; ii < types; ii++)
			{
				sw.WriteLine("{0},{1}", food[ii].Type, food[ii].Calories);
			}
			sw.WriteLine("");
		}
	}
}

Posted 31-Mar-17 11:11am

imeyal0

Updated 31-Mar-17 13:22pm

Patrice T

v5

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Comments

CHill60 31-Mar-17 17:15pm

Your question is not clear. Use the Improve question link to describe your problem

[no name] 31-Mar-17 17:17pm

You have already been told what to do. A bit of logical thinking will help you. If you update all of your objects at the same time, what else would you expect to happen?

imeyal0 31-Mar-17 17:19pm

please help and assist. I also tried to update at different days but the result is the same

j snooze 31-Mar-17 17:21pm

well I can't see what your UpdateCalories does, but if you don't have a method called updatecalories i'd say that's your problem. Also your code should be written to be more maintainable. Where you have
foods.Add(food[0]);
foods.Add(food[1]);
foods.Add(food[2]);
what happens when there are 50 food types? are you going to write 50 lines of code and recompile for every food type added?
It should be
for(int i=0; i<food.length;i++){
foods.Add(food[i]);
}
if the above is just a sample thats fine but if you plan on making a real app out of this, I highly recommend the for loop .

imeyal0 31-Mar-17 17:23pm

updatecalories is there.
yes..It is just a sample.
please help and assist. I also tried to update at different days but the result is the same

Patrice T 31-Mar-17 17:28pm

What output do you get ?
What output do you want ?

imeyal0 31-Mar-17 17:29pm

got this:
Day0
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

Day1
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

Day2
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

Day3
protein,5.3
vitamins,6.3
Carbonhydrate,7.3
----------------------------------------
But I want this:
Day0
protein,2.0
vitamins,3.0
Carbonhydrate,4.0

Day1
protein,3.1
vitamins,4.1
Carbonhydrate,5.1

Day2
protein,4.2
vitamins,5.2
Carbonhydrate,6.2

Day3
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

-----------------
I still want to have access to the values of the previous days not just the last day.

Patrice T 31-Mar-17 18:06pm

Use Improve question to update your question.
So that everyone can pay attention to this information.

Add the piece of code that produce actual result. something that we can run.

imeyal0 31-Mar-17 19:04pm

I have added the code

imeyal0 31-Mar-17 19:41pm

I have used it - also gave the same wrong output as before.

imeyal0 31-Mar-17 19:50pm

when i tried what you suggested- it worked. But with that I will not have access to re- use the values of previous days. Please assist further.
Many thanks.

imeyal0 31-Mar-17 19:58pm

thank you guys for the effort. The main this is that I need to be able to retain the daily calories values to be used for other calculations. Printing to output will only come after everything is done.

Patrice T 31-Mar-17 20:45pm

For discussion about an solution, use the button "Have a Question or Comment?" on bottom of solution.
It is easier to follow.

imeyal0 5-Apr-17 6:59am

Hello, Please how do i send the output to an Excel/CSV file instead of a text file. Please kindly help.

Patrice T 5-Apr-17 7:12am

You'd better ask a new question, so everyone will be aware.

j snooze 31-Mar-17 17:32pm

ah...now I see the issue. If you pass that list to another method the default is byval (or just a copy of it) so you are only updating the "handed off to" variable in the Updatecalories method. You can do this 2 ways, but you still have to figure out a way to store the list for each separate day unless I'm misunderstanding what you are trying to do because its not real clear.

Either pass the list byref so your method would have to be defined as
(Solution 1)
public void UpdateCalories(byref List<foood> foodItem){
////keep current code
}

Or
(Solution 2)
public List<foood> UpdateCalories(List<foood> foodItem)
{

for (int i = 0; i < foodItem.Count; i++)
{
foodItem[i].calories = foodItem[i].calories + 1.1;
}

return foodItem;
}

your for loop that calls the method would then need to do this

for (int i = 0; i < days; i++)
{

foods = UpdateCalories(foods);

}

j snooze 31-Mar-17 17:34pm

I just saw the output you need, to do that you either have to store each day in a list of its own, or output the data in your updatecalories method on the fly and not worry about storing it in a list.

imeyal0 31-Mar-17 17:37pm

I tried solution 2 before now but did not work. Also, i store each day in List of list.

I will try solution 1 now and get back asap.

imeyal0 31-Mar-17 18:23pm

i got the same result
Day0
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

Day1
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

Day2
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

Day3
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

but i want this:
---------------------------
But I want this:
Day0
protein,2.0
vitamins,3.0
Carbonhydrate,4.0

Day1
protein,3.1
vitamins,4.1
Carbonhydrate,5.1

Day2
protein,4.2
vitamins,5.2
Carbonhydrate,6.2

Day3
protein,5.3
vitamins,6.3
Carbonhydrate,7.3

imeyal0 31-Mar-17 18:27pm

using (StreamWriter sw = new StreamWriter(@"U:\Food\food.txt"))
{

//sw.WriteLine("");

for (int i = 0; i < days; i++)
{

{
sw.WriteLine("Day" + "{0}", i + 1);

for (int ii = 0; ii < types; ii++)
{

sw.WriteLine("{0},{1}", foodDays[i].foods[ii].Type, foodDays[i].foods[ii].Calories);

}
sw.WriteLine("");
}

}

}

imeyal0 31-Mar-17 18:45pm

please how to make the property (calories) of an object not reference type. so that once it is changed, it will not affect all the other days

2 solutions

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j snooze · Answer 1 · 2017-03-31T11:57:00

public class Foood
       {
           public string Type { get; set; }
           public double Calories { get; set; }

           public Foood(string type, double calories)
           {
               Type = type;
               Calories = calories;
           }
       }

       public class Days
       {
          public List<Foood> foods = new List<Foood>();
       }

       private void testit()
       {
           int types = 3;
           List<Foood> foods = new List<Foood>();
           List<Days> foodDays = new List<Days>();
           int days = 3;


           Foood[] food = new Foood[types];
           food[0] = new Foood("protein", 2.0);
           food[1] = new Foood("vitamins", 3.0);
           food[2] = new Foood("Carbonhydrate", 4.0);

           for (int i = 0; i < food.Length; i++)
           {
               foods.Add(food[i]);
           }

           Days day = new Days();
           day.foods = foods;
           foodDays.Add(day);

           for (int i = 1; i <= days; i++)
           {
               day = new Days();
               day.foods = UpdateCalories(foodDays[i-1].foods);
               foodDays.Add(day);
           }

       }

       public List<Foood> UpdateCalories(List<Foood> foodItem)
       {
           List<Foood> newFood = new List<Foood>();
           Foood item;

           for (int i = 0; i < foodItem.Count; i++)
           {
               item = new Foood(foodItem[i].Type, foodItem[i].Calories + 1.1);
               newFood.Add(item);
           }

           return newFood;
       }
   }

Patrice T · Answer 2 · 2017-03-31T13:22:00

Solution 2

try this code

C#

using (StreamWriter sw = new StreamWriter(@"U:\Food\food.txt"))
{
	for (int i = 0; i < days; i++)
	{
		sw.WriteLine("Day" + "{0}", i);
		for (int ii = 0; ii < types; ii++)
		{
			sw.WriteLine("{0},{1}", food[ii].Type, food[ii].Calories);
		}
		sw.WriteLine("");
		//	UpdateCalories here
	}
}

[Update]
Another way to see the problem is:
day 0, use good values
day 1, use good values + 1.1
day 2, use good values + 1.1 * 2
day 3, use good values + 1.1 * 3
...
and you don't change food values.

C#

sw.WriteLine("{0},{1}", food[ii].Type, food[ii].Calories + 1.1 * i);

Posted 31-Mar-17 13:22pm

Patrice T

Updated 1-Apr-17 4:11am

v4

Comments

imeyal0 1-Apr-17 5:03am

thanks for your help. I really need the calories for all the days before i get to the stage of printing out the output.

imeyal0 1-Apr-17 10:03am

I think the assistance i need is to be able to work with a duplicate Object from one day to the next without altering/changing the changing Original object

imeyal0 1-Apr-17 13:15pm

please kindly assist - the Designer View for form 1 in CSharp Visual Studio 2015 is missing. It only appears when i click the start button. Please how do i bring it back in order to edit the form.
I think it got missing whilst copying from one VS version to the other and using different computers.

Patrice T 1-Apr-17 13:49pm

I gave you help on things I know.
I don't use VS

imeyal0 1-Apr-17 16:06pm

Many thanks. I really appreciate.