Difference between vectors in C++

Difference between vectors in C++

Difference between vectors in C++

In C++, the vector is a dynamic array that can grow in size. The three declarations you’ve provided are different ways to declare a vector, and here’s what each one means:

1. vector<int> result;

• This declares a vector named result that will store integers (int). Initially, it is empty, and its size will grow dynamically as integers are added to it.

2. vector<int> result[10];

• This is actually an array of vectors. It declares an array named result with 10 elements, where each element is a vector that can store integers. Each vector in the array can grow independently in size.

3. vector<int> result(nums.size());

• This declares a vector named result that will store integers, and it is initialized to have a size equal to nums.size(). Assuming nums is another vector, result will have the same number of elements as nums from the start.

In summary:

• The first declaration is a single vector with a dynamic size.
• The second is an array of 10 vectors, each with a dynamic size.
• The third is a single vector whose initial size is set to the size of another vector, nums.

Here’s how you might visualize the differences:

    // A single empty vector that can grow dynamically.
vector<int> result;
    // An array of 10 vectors, each can grow dynamically.
vector<int> result[10];
    // A single vector initialized to the size of 'nums'.
vector<int> result(nums.size());
 

Remember, the second declaration is not a vector but an array of vectors, which is a common point of confusion. The third declaration assumes that nums is a previously defined vector and uses its size to initialize the result vector. I hope this clarifies the differences for you! If you have any more questions or need further explanation, feel free to ask.