I need to write a function that merges 2 double arrays together into a single array. How would I go about doing that?

EDIT:
I have 2 arrays that like this for example: ´double arr1[] = {3.75, 4, 2.6}´ and ´double arr1[] = {6.9, 7.866}´ and I need to find a way to merge these 2 together. Since I have literally no clue how to do that I dont even know if its easier to merge the 2 together in a seperate arr3 or if its easier to somehow append arr2 onto arr1.