If you do a google search you can find it yourself...
You're outputting "Hello" on the screen but since the function main has to return an integer (you said that when you named the function "int main()") you return 0 (meaning that the function has succeed)
But if the function doesn't work, the exit function will end it up and return a code error 10
I'm more than happy to help but sometimes I wish that people would use Google a bit.
Edit: Seems that ParkinT was quicker than me