Start off with an n value that allows you to enter the while loop. The while loop should continue as long as n is not 1 or 2. After the while loop is over, you know n is either 1 or 2, so just test the n value and assign x accordingly.
n = 0;
while sum(n==[1 2])<1,
n = input('Please input value for n:\n');
end
if n==1
x = 0;
else
x = 7;
end
