加速VB.NET应用程序到Excel

I have written a VB.NET application in Visual Studio 2015. (first time ever had any contact with visual basic or VS). The application takes an input csv file, analyses it and splits it according to that analysis into 2 output csv files. For one of these output files, I then need to change every blank cell to have the value of zero. My prob, is that the code i've made is processing 750 input csv files to produce 1500 output files and each process in the loop is taking 5 mins meaning it's taking up to 5 days to run!! That is too long!I have written a VB.NET application in Visual S