Good Question!
While they may seem similar the truth is alligators and crocodiles are very different creatures. To begin, they come from different families of crocodilians; alligators come from the alligatoridae family, which includes the alligator and the caimans and crocodiles come from the crocodylidae family. They also have distinctively different jaw shapes; alligators have a wide rounded snout that looks a little like a shovel, whereas crocodiles tend to have longer and more pointed "V"-shaped noses. They also have different teeth placement, as well as a few different glands (but this would not be possible to detect by simply looking at one.)
It may make sense to think of them as cousins; both of their families branch out from the crocodilians so they are related in a way, but they are not as similar as siblings (or creatures from the same exact species) would be.
This question is something that my brother, and I think almost every pre-teen boy I know has wondered about at some time (as well as some of the girls I'm sure, but I doubt as many of them actually wondered aloud). So, to answer this question once and for all: no, a burp and a fart are not the same thing just from different ends of the body.
On one end, bacteria in the intestines break down food particles and produce methane and sulfur dioxide in the process, these gases eventually then become a fart. Gases also exist in your intestine from swallowed air and gas seeping into the intestines from the blood - but once the gas is in your intestine it has to come out that end, it cannot migrate to the stomach to become a burp.
On the other end, burping is caused by excessive gas in the stomach which is also made in the process of breaking down food particles, but it is made by digestive acids rather than intestinal bacteria. They may seem similar but they really are not, they don't even have the same chemical composition: farts have less atmospheric gas content and more bacterial gas content than burps.
As for the second part of your question, I think its pretty obvious that, since they are so different, holding one back will not cause the other to occur. So now we can all stop wondering.
Jill's comment: The boiling point for water occurs when the pressure of the water molecules (that move faster as they gain heat energy) equals the pressure of the air that surrounds it. By this logic, if you increase the pressure of air then the water temperature will continue to increase until it reaches it - the boiling point is not the same in every location and it can be changed. So yes, water can get hotter than the boiling point although eventually evaporation will cause it to turn into water vapor and eventually cool.
Jill's comment: Assuming you're asking me about zero degrees Celsius, which is the same as 32 degrees Fahrenheit, all you have to do is convert the temperature to Fahrenheit and discover that tomorrow would be 16 degrees Fahrenheit. If you're asking this question assuming it is zero degrees Fahrenheit outside, its also simple: we convert to Celsius, minus 17.7 degrees, and double that to get negative 31.5 degrees Celsius. This answer would work if you had said: "today it will be zero degrees and tomorrow the temperature will be twice as low, what will it be then?" However, you said "it's going to be twice as cold," and that is something completely different.
The way this question is posed asks us to focus on this issue of heat (energy). According to Bob Weinbeck of the American Meteorological Society's Education Office, "cold is really the presence of minimal heat. Temperature only reflects the amount of heat - and on an arbitrary scale. One could use the absolute temperature scale." The Absolute Temperature Scale is a scale that begins at absolute zero, or the temperature at which there is no molecular motion. The most common absolute scale is the Kelvin (K) scale, which is based on the Celsius scale.
On the Kelvin scale, minus 273.16 degrees C is equal to 0 degrees K. "Twice as cold would mean only half the heat energy," Weinbeck says. "So that the absolute temperature would be half of 255.46 K or 127.73 K. Such temperatures would certainly shiver your timbers!" Converted back to Celsius this answer to the 'twice as cold' dilemma would make our temperature tomorrow minus 145.43 degrees, which is a great deal colder than the world record cold of minus 89.6 degrees C which was set July 21, 1983 at the Russian Vostok Station in Antarctica!
Basically: This question can be answered in many ways, but they all come out to near-impossible, if not impossible to reach temperatures: you'll never have to worry about it being twice as cold as zero outside.