In addition to what marto said, I would state that your requirement is really not clear:

- Do you want to write a C program or a Perl program? If you want to have C code, then you probably chose the wrong forum. Either way, you might want to start with good book for beginner and first try to solve your problem by yourself.

- I have no idea what "replace a charecter with another position based on its postion" means and your purported example is as limpid as mud. A good example should state the input, the output and often an explanation on how to get from the input to the output.

Please clarify.

Update: fixed a small typo.