Checking Character Length in a specific row and column

Hi, I'm still a noob when it comes to excel programming and I'd like to ask if there is any way where I can automatically choose to check the character length of a specific row?

I have an excel sheet with 20 columns ranging from column A-T. each column has a specific character restriction such as A can only have 3 characters, B can have 4 etc. until T. These columns are considered as Headers that needs to be checked if the number of characters they have are correct.

However, I have a lot of Headers in that Worksheet that needs to be checked and the number of rows where each header may start is not predefined. Meaning, a header may begin at row4,row9,row11,row20 etc.

I know I need to make a loop, but the problem is, I don't know how to increment my column from Column A to column B etc so that I can check each cell's character length. I need to increment my Column 20times and then check the character length, afterwards I need to go to the next row until I encounter another header and then check the columns again.

Can someone please tell me how I can increment the column and go to the next row? I'd really appreciate any help. :D