C#.NET Stack (non-generic): is the following mixed-type Push() usage valid? Stack st = new Stack(); st.Push("hello"); st.Push(8.2); st.Push(5); st.Push('b'); st.Push(true);

Introduction / Context:
The classic System.Collections.Stack is a non-generic last-in, first-out collection that stores elements as System.Object. This permits mixing types in the same collection, which is sometimes useful and sometimes risky.

Given Data / Assumptions:

• We are using System.Collections.Stack (non-generic), not Stack.
• We push strings, floating-point numbers, integers, a char, and a bool.

Concept / Approach:
Because the non-generic Stack stores elements as object references, any type can be pushed (value types are boxed automatically). Type safety is enforced at use-sites via casts when popping or peeking.

Step-by-Step Solution:

Verification / Alternative check:
Run-time: foreach over st will yield objects of different types. Casting back to original types works as long as you cast correctly (or check with 'is'/pattern matching) before use.

Why Other Options Are Wrong:
A/D assume homogeneity requirement or a special API—non-generic Stack has neither. B forbids bool—false. C confuses char vs. string; 'b' is valid for char.

Common Pitfalls:
Mixing types can lead to InvalidCastException when popping if you assume the wrong type. Prefer Stack for compile-time safety.

Final Answer:
Valid: non-generic Stack stores objects, so dissimilar elements are allowed.