Perhaps you've read posts like Falsehoods Programmers Believe About Names and Falsehoods programmers believe about time. Maybe you've also read Falsehoods programmers believe about geography.

Addressing is a fertile ground for incorrect assumptions, because everyone's used to dealing with addresses and 99% of the time they seem so simple. Below are some incorrect assumptions I've seen made, or made myself, or had reported to me. (If you want to look up an address for a UK postcode or vice-versa to confirm what I'm telling you, try the Royal Mail Postcode Finder)

An address will start with, or at least include, a building number. Counterexample: Royal Opera House, Covent Garden, London, WC2E 9DD, United Kingdom.

When there is a building number, it will be all-numeric. Counterexample: 1A Egmont Road, Middlesbrough, TS4 2HT 4-5 Bonhill Street, London, EC2A 4BX

No buildings are numbered zero Counterexample: 0 Egmont Road, Middlesbrough, TS4 2HT

Well, at the very least no buildings have negative numbers Guy Chisholm provided this counterexample: Minusone Priory Road, Newbury, RG14 7QS (none of the databases I've checked render this as -1)

We can put those funny numbers into the building name field, as no buildings have both a name and a funny number Counterexample: Idas Court, 4-6 Princes Road, Hull, HU5 2RD

When there's a building name, there won't be a building number (or vice-versa) Counterexample: Flat 1.4, Ziggurat Building, 60-66 Saffron Hill, London, EC1N 8QX, United Kingdom

A building number will only be used once per street The difference between 50 Ammanford Road, Tycroes, Ammanford, SA18 3QJ and 50 Ammanford Road, Llandybie, Ammanford, SA18 3YF is about 4 miles (Google Maps).

When there's line with a number in an address, it's the building number. Counterexample: Flat 18, Da Vinci House, 44 Saffron Hill, London, EC1N 8FH, United Kingdom You also get suite numbers, floor numbers, unit numbers, and organisations with numbers in their names. Adrien Piérard contributes an address from Japan with fifteen digits in six separate numbers (five if you count the zip code as a single number). The format is: 980-0804 (zip code), Miyagi-ken (prefecture) Sendai-shi (city) Aoba-ku (ward) Kokubuncho (district) 4-10-20 (sub-district-number block-number lot-number) Sendai (building name) 401 (flat number).

OK, the first line starting with a number then Counterexample: 3 Store, 311-318 High Holborn, London, WC1V 7BN

A building will only have one number Benton Lam offers this address from the Hong Kong Special Administrative Region - it has both a number on its road (14) and in its group of buildings (3): 15/F, Cityplaza 3, 14 TaiKoo Wan Road, Island East, HKSAR

The number of buildings is the difference between the highest and lowest building numbers Tibor Schütz points out building numbers may be skipped - for example, on a street where even-numbered buildings are on one side, odd numbers on the other; multiple buildings sharing the same number (such as where a new house has been built) and buildings with more than one number. Cyrille Chépélov and Sami Lehtinen tell me in Antibes, France and rural Finland some buildings are numbered based on the distance from the start of the road - such as Longroad 65 for the building 750m from the start of longroad.

If the addresses on the left of the road are even, the addresses on the right must be odd Cyrille Chépélov points out that in places, Boulevard Théophile Sueur, Montreuil, Seine-Saint-Denis, France has evens-only on both sides. The two sides are also in different cities and Départements.

A building name won't also be a number Ben Tilly reports on Ten Post Office Sq, Boston MA 02109 USA - which is not, reportedly, the same as 10 Post Office Sq, Boston MA 02109 USA.

Well, at least you can omit leading zeros Shaun Crampton reports living at 101 Alma St, Apartment 001, Palo Alto - where apartments 1 and 001 were on different floors.