Trace the output of the following C# code. int[] nums = new int[3] {1, 2, 3}; nums[0] = 4; MessageBox.Show(nums[0].ToString());

Question

BlackTom AI · Accepted Answer

Let’s walk through the code and each option with careful attention to how arrays and indexing work in C#.
First, the statement int[] nums = new int[3] {1, 2, 3}; creates an array of three integers and initializes it with the values 1, 2, and 3 in that order. The array indices start at 0, so nums[0] refers to the first element in the array, which currently is 1.
Next, the line nums[0] = 4; assigns the value 4 to the element at index 0. After this assignment, the array becomes {4, 2, 3}.
Finally, MessageBox.Show(nums[0].ToString()); converts the first element of the array to a string and displays it. Since nums[0] now holds 4, ToString() yields "4".
Now let's evaluate each option:
- Option a: "4" — This matches the value stored at nums[0] after the assignment, so it correctly reflects the program’s output.
- Option b: "Error" — There is no runtime or compile-time error evident in these statements. The array is properly declared, assigned, and accessed within bounds, so this option is incorrect.
- Option c: "2" — This would have been true if we had not modified nums[0]. It represents the original first element before the assignment, which is no longer the case.
- Option d: "1" — This would be the initial value at nums[0] prior to the reassignment, but since we changed it to 4, this option is incorrect.
In summary, understanding that nums[0] changed from 1 to 4 and that the ToString call reflects the updated value is the key to selecting the correct option.

Trace the output of the following C# code. int[] nums = new int[3] {1, 2, 3}; nums[0] = 4; MessageBox.Show(nums[0].ToString());单项选择题

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