Explain the difference between a function declaration and function definition.   

Function declaration and Function definition: 

A function declaration having the name of the function, a list of variables that must be passed to it and the type of variable it returns, if any. For instance in the following program in line 2, the function cube is declared. The variables to be passed to the function are known as arguments, and they are enclosed in parentheses following the function's name. In this instance, the function's argument is long x. The keyword before the name of the function shows the type of variable the function returns. In this case, a type long variable is returned. The function itself is known as the function definition