Question

                var names = new[] { 
                            new { Name = "John", Age = 44 },
                            new { Name = "Diana", Age = 45 },
                            new { Name = "James", Age = 17 },
                            new { Name = "Francesca", Age = 15} 
                            };

            for (int i = 0; i < names.Length; i++)
            {
                names[i].Age = 23; //-------->Error
                names[i] = new { Name = "XYX", Age = 26 }; //----->Works fine
            }

            foreach(var name in names)
            {
                name.Age = 1;  //-------->Error
                name = new { Name = "ABC", Age = 25 };  //-------->Error
            }

I have two questions here.
1. Why I was not able to change the any attribute of an iteration variable.
2. I was only able to assign a new object to the iteration variable in for loop. Not in foreach loop. Why?

Answer 1

Question 1: Why I was not able to change the any attribute of an iteration variable?

From the documentation on Anonymous Types:

Anonymous types provide a convenient way to encapsulate a set of read-only properties

You cannot change the values of the properties in your anonymous type, so

name.Age = 1;
// and
names[i].Age = 1; 

are equally invalid.

---

Question 2. I was only able to assign a new object to the iteration variable in for loop. Not in foreach loop. Why?

From the documentation on IEnumerable:

An enumerator remains valid as long as the collection remains unchanged.

You would invalidate the iterator if you change the backing list in any way. Consider what would happen if the iterator returned the items in a specific order based on the Age field, for example.