C :: Program To Match Strings From Input To Files Using Dfa

'Write a program to match the user input string with the contents of text files and give the result as to which files contain the input string. This has to be done by using finite automaton.' (Any language can be used) So basically, the user will input a string (in the command line or a gui) and "we must pass the text files to the DFA" (I'm double quoting this because it's precisely what my professor told) and then display those files which contain the string. The string can be hard-coded, ie,the user will get the output file that contains a specific string. ex: 'hello'. The problem is, I have never done any program on DFA so I'm at a loss. how to write the program. Should I read the files first and then use some 'switch' or 'goto' conditions for the DFA? Below is a code I found on the internet for simulating a DFA accepting a specific string.

Code:

s: accept = false; cin >> char;
if char = "m" goto m;
if char = EOF goto end;
goto s;
m: accept = false; cin >> char;
if char = "m" goto m;
if char = "a" goto a;
if char = EOF goto end;
goto s;
}

[code]....