3 changes:
1. In the enlarge part, I didn't change because I didn't find a good way to deal with the local variable and the clear definition. malloc is commonly used in LeetCode so I think it is not bad for a beginner.
2. I changed the initialization of the second array to make it in the same style as C++.
3. In the enlarge part in main, I deleted the code of pointer free to match the array operations. I also changed the operate array in the later part because the enlarged array cannot be assigned to the older array name.
BTW, sorry for updating so late. Reading different version documents and book are really tiring and boring.
