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);
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AInvalid: a Stack cannot store dissimilar elements like "hello", 8.2, and 5.
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BInvalid: Boolean values cannot be stored in a Stack.
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CInvalid: the fourth call must use "b" instead of 'b'.
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DInvalid without a special PushAnyType() method.
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EValid: non-generic Stack stores objects, so dissimilar elements are allowed.
Answer
Correct Answer: Valid: non-generic Stack stores objects, so dissimilar elements are allowed.
Explanation
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:
Check string → allowed (reference type).Check double/float literal → allowed (boxed value type).Check int → allowed (boxed value type).Check char literal 'b' → allowed (boxed value type).Check bool → allowed (boxed value type).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
Final Answer:Valid: non-generic Stack stores objects, so dissimilar elements are allowed.