When a two-dimensional array is passed as an actual parameter, the number
of columns of the actual and formal arrays must match.

Question

BlackTom AI · Accepted Answer

Because element addressing in a contiguous 2D array uses the number of columns (the second dimension) as the stride, the function’s formal parameter must match the actual array’s column count.

1. Relevant knowledge points and concepts
- In languages with row-major contiguous 2D arrays (C/C++ style), a 2D array int A[R][C] is laid out as R blocks of C consecutive elements.  
- The compiler computes the address of A[i][j] as base + ((i * C) + j) * sizeof(element).  
- When a function parameter is declared as int B[][C2], the compiler uses C2 to compute offsets inside B.

2. Step-by-step reasoning
- Suppose actual array is int A[3][4]. The compiler expects 4 columns when computing offsets: address of A[2][3] = base + ((2*4) + 3)*sizeof(int) = base + 11*sizeof(int).  
- If the function parameter is declared int F(int X[][5]) (i.e., C2 = 5), the compiler will compute address of X[2][3] as base + ((2*5)+3)*sizeof(int) = base + 13*sizeof(int).  
- The two computed addresses differ, causing incorrect memory access and undefined behavior.

3. Intermediate calculation example
- Actual: (2*4)+3 = 11 -> offset 11*sizeof(int).  
- Mismatched formal: (2*5)+3 = 13 -> offset 13*sizeof(int).

4. Why the correct answer is correct
- Because the compiler must know the column stride to translate X[i][j] to a linear offset, the formal parameter’s second dimension must match the actual array’s number of columns (unless you use alternative parameter types like pointers and manual indexing).

5. Why the other option is incorrect
- "False" would imply column counts can differ without consequence. That is incorrect for contiguous 2D arrays: mismatched column sizes produce wrong offsets and undefined behavior. (Note: some languages/representations—e.g., Java’s jagged arrays or higher-level containers—behave differently, but the statement refers to the usual contiguous 2D array parameter passing.)

6. Conclusion
- Therefore the statement is True. This matches the provided answer: True.

When a two-dimensional array is passed as an actual parameter, the number of columns of the actual and formal arrays must match.判断题

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