How would you declare and initialize a two-dimensional array of 3x3 with zeros?

• A. int mat[3][3] = {0, 0, 0};
• B. int mat[3][3] = 3;
• C. int mat[3][3] = {0};
• D. int mat[3][3][3] = {0};

Answer: (C)

The key idea here is how aggregate initialization works for multi-dimensional arrays in C: if you provide fewer initializers than there are elements, the remaining elements are automatically set to zero. Declaring a 3-by-3 int array and using a single zero to initialize it takes advantage of that rule. You set the first element, mat[0][0], to 0, and because there are no more initializers, every other element in the array (the rest of the first row, the other rows) is initialized to zero as well. This makes the entire 3x3 matrix zeros in a clear and concise way.

Options that place specific values for the first row or introduce an extra dimension either complicate the initialization or change the array’s type. For example, providing three zeros initializes the first row and leaves the rest zero as well, but it’s less straightforward to read. Using a single value for a 2D array isn’t valid as an initializer in this context, and adding another dimension declares a 3D array, which isn’t what’s asked.