When you do a scanf() it's taking the value you ask for only.. for example:
scanf("%d",&posothta);
Let's say I enter 5 here. Really, stdin got 2 characters: '5' and '\n' (because I had to hit the enter key and that generates a newline character).
So into posothta goes the 5, but that pesky newline is left sitting there. The next scanf() now is looking for a character, and since the newline character ('\n') is indeed a character, the program doesn't ask questions, it simply picks up that newline and moves on.
Change your code to:
scanf(" %c",&eidos);
Will skip tell scanf() that "I want you to skip any whitespace characters, then grab the next one". To scanf() a white space character includes not only spaces, but newlines as well.
