Outside of a for-loop, x in range(..) mean something different. It's a test that returns a boolean

print(1 in range(1,11)) # prints True

So your while-loop actually means this:

def main():
  x=1;

while True if x in range(1,11) else False:
     print (str(x)+" cm");


if __name__=="__main__":
    main();