Why 42 is used..?

Question

int myArr[5];
for(int x=0; x<5; x++) {
myArr[x] = 42;
}

Answer 1

'42' is the universal answer of all questions ^^ (answer to the ultimate question of life, the universe, and everything)
It's a reference to << The Hitchhiker's Guide to the Galaxy >>
https://en.m.wikipedia.org/wiki/Phrases_from_The_Hitchhiker%27s_Guide_to_the_Galaxy

Answer 2

https://en.m.wikipedia.org/wiki/42_(number)