It's more a rotate than shift. You need to save the last value when you start (9 in this case), shuffle all the elements into the next slot up starting with the second to last. Then set the saved value into position zero.
Your main's logic is correct, but syntactically incorrect. main should always return an int.
For one thing, your shiftright() function isn't even doing anything they way you have it defined. It's just iterating through the array. Also, why did you say you wanted to shift everything to the left, but you called your function shiftright() ??
You didn't say what you wanted to do with the last value, so like kdw, I'm assuming you want to throw the value of the first element onto the end.
If I were you I'd go above and beyond and make the function more generic. Write it so that the user can specify how many places to rotate or follow the example of std::rotate where you specify where you want a particular position moved to.