For example, if you had a batch file called stuff.bat and you typed stuff a b c d at the command prompt, the letters a, b, c, and d would be assigned to the variables %1, %2, %3, and %4, respectively.
Fiberglass shingles generally have a longer life expectancy than do asphalt shingles. Properly installed tiled roofs have a normal useful life of 20-30 years or longer, but individual pieces can become cracked or broken or the nails rust out.
20 Year shingles rarely last 20 years without leaks. In my area where it is very hot in the summer and exposed to a lot of sunshine in all seasons, 20 year roofs are good for about 12 years usually. There are maintenance things you can do to prevent leaks, but not a lot you can do about aging of the shingles.