C#.NET — Which declarations correctly define a 2×3 rectangular array?

Difficulty: Medium

1) int[, ] a; a = new int[2, 3] { {7, 1, 3}, {2, 9, 6} }; 2) int[, ] a; a = new int[2, 3] { }; 3) int[, ] a = { {7, 1, 3}, {2, 9, 6} }; 4) int[, ] a; a = new int[1, 2]; 5) int[, ] a; a = new int[1, 2] { {7, 1, 3}, {2, 9, 6} };
1, 3
2, 3
2, 4, 5
4, 5

Correct Answer: 1, 3

Explanation:

Introduction / Context:
Rectangular arrays in C# specify sizes for each dimension. They can be initialized either with an explicit new int[rows, cols] { ... } or with an implicit = { ... } initializer at declaration time.

Given Data / Assumptions:

Target array shape is 2 rows × 3 columns.
We evaluate five candidate declarations/assignments.

Concept / Approach:
For rectangular arrays, both of the following are valid: explicit allocation with matching initializer sizes, and declaration with an immediate initializer omitting new int[,]. Incorrect cases either specify wrong dimensions or provide invalid/empty initializers.

Step-by-Step Solution:

1) Valid — explicit 2x3 allocation with a 2×3 initializer.2) Invalid — empty initializer braces are not allowed for a sized array.3) Valid — declaration with initializer infers 2x3.4) Invalid — dimensions are 1×2, not 2×3.5) Invalid — allocation says 1×2 but initializer is 2×3; size mismatch.

Verification / Alternative check:
Try compiling each snippet; only (1) and (3) succeed for a 2×3 rectangular array.

Why Other Options Are Wrong:

2: Empty initializer with fixed size is invalid.
4/5: Dimensions do not match the required 2×3 (and 5 also conflicts with its own initializer).

Common Pitfalls:
Mixing rectangular arrays with jagged array initialization rules and forgetting zero-based indexing.

Final Answer:
1, 3

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C#.NET — Which declarations correctly define a 2×3 rectangular array?

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