External functions can be called via external function calls.
A function in solidity can be marked as a constant. Constant functions cannot change anything in the contract; they only return values when they are invoked and do not cost any gas. This is the practical implementation of the concept of call as discussed in the previous chapter.
The syntax to declare a function is shown as follows:
function <nameofthefunction> (<parameter types> <name of the variable>)
{internal|external} [constant] [payable] [returns (<return types> <name of the variable>)]
