Need help with C programing Linux

[serialcek]

Hello everyone!
First of all sorry for my bad English.

I'm trying make a program Linux terminal in C.
I want that in this my terminal people can be able to to chose Windows,Linux or Mac commands to write..
When they run my program it will ask them which input method they wanna use (Linux, Windows, Mac) and then if they choose Mac they will be able to write Mac commands in terminal which runs in Linux and the commands will be recognized.

I'm trying to do some terminal emulator which works in linux.
All I got for now is a program which simulate the Linux terminal which means that it works only for linux commands.
The problem is that I didn't write it so I need some help to understand everything in the code.

Here can zoo download the code:
http://www.mediafire.com/?kp7f1y03827jgvf

I'm sorry for the comments in Slovene. If anyone need the translated comments I will translate then.

So in this my code I don't understand why it has to be compiled with this words:
gcc -Wall -ansi -pedantic -o fsh main.c

What does the ansi and pedantic mean?
And the other thing in line 151:

execvp(*exec_argv, exec_argv);

Is this the way that we run the command that the user wrote?
Is execvp the function that run our command?

That's for now all..
Thx

[ne555]

gcc supports some features that are not compatible with the standard. By instance long long (c++) or typeof
Those flags will turn them off, making compile errors (or warnings) if you use them.
More info man gcc

IIRC exec will replace the program with the command (that is why you forked before).