Create a program that processes text file according to task variant. Additional requirements:

1. A program user inputs name of file.

2. Program outputs content of file before and after modification of file.

3. Program should output text message in case of errors. 4. Program has to be written in C

Considering :

Given a string S and a text file, find the specified string and, if such string exists in the file, return its position (line number and position in this line).