C# get user input(offset) & (write new value to offset)

Question

Hello

After trying for hours and googling around i give up, also used the search here and couldn't find anything that i'm looking for.

I'm trying to make a windows form application where the "user" can enter a offset & new value to be written to the offset.

I've been trying to do it with Console.ReadLine(is there a better way?) and 2 textbox but it kept writing 0x00000000

Example1:

Textbox1>Offset: 0x00001234
Textbox2>Value: 9A05FF80
http://i.imgur.com/733ySBV.jpg

also how about this? instead of offset+value it would be find&replace.

Example2:

Textbox1>Find: whatever the user inputs (example: 6316707C6301947C6307B4E80100C07C)
Textbox2>Replace: whatever the user inputs as new(example: 1F011F3751F5FBA34719F514236FB1B3)

Best Regards