Score

Explanation
This is a built in variable that holds the score for your game, there is no need to declare it.

Example
This will add 5 to the number already in the score variable. So if score was 10, score would now be 15:

score += 5;
This will set the score to 5.

Remarks
Note that internally score is stored as 4-byte integer with range -2147483648 to 2147483647. However setting it to value like 3000000000 just makes it negative due to integer overflow.