Pointers and arrays of C

Start by looking at your error messages: they are in perfectly good English, and are - surprisingly - very clear.

prog.c:3:6: warning: return type of ‘main’ is not ‘int’ [-Wmain]
 void main(void)

Correct: you have written it as void function. Change "void main" to "int main" and return zero at the end of the function.

prog.c:9:3: error: expected ‘;’ before ‘for’
   for (i = 0; i < 4; i++)

So look at your code:

pa = a
  for (i = 0; i < 4; i++)

It's not wrong: where is the semicolon between the two commands?
And so forth...

Read the messages. Think about what they say.
Don't just go "it didn't work" or you will get nowhere - getting it to compile is the easy bit! After that, you have to get it to work, and that's a lot harder.