Hello World! 
I'm talking about functions in C++
You have already used some functions such as sqrt and pow that are in the math library. 
The function sqrt requires 1 argument. 
When you call sqrt  you pass it one value  and the function returns the square root. 
When we call sqrt and pass it 100, it returns 10.
Function pow receives two values and returns the first value to the power of the 2nd value. 
Lets write a function that receives a number and returns half of it.
We will make it return a double and it will need one argument.
We can use the function half anywhere we could use a double value.
Because the function returns a value, we can use it in a cout statement.
We can assign its value to a variable: n=half(num);
We can use it in a Boolean expression: if (half(num)>100
Ok, now you try it!