How to merge the vector_elements of two .csv files in series in one csv file in c++?

First file, file1.csv

4.00

3.00

3.00

4.00

Second file, file2.csv

10.8

12.4

21.9

17.5

I want my final file final.csv in the format

4.00

3.00

3.00

4.00

10.8

12.4

21.9

17.5