Writing Functions

The Big Idea What if this was how we did powers?

The Big Idea Functions provide Code Reuse Abstraction

Information Function header specifies everything but job of function A contract to do work

Review A function declaration : Header Body : Statements that do work of the function

A Function A function: -Called max -Takes two inputs (ints) -Gives back an int

Using Max Using Max:

Full Program Must declare a function before it is used

Function Name Function name Normal identifier rules Use camelCase no spaces, can't start with number, etc… Use camelCase Clearly identify job Readability > terseness Focus on verbs

Body Body of a function – where magic happens Always a block of code { } Has own scope Variables declared inside only available inside

Parameters Parameters : information function needs type name, type name, type name… OK to have no parameters int getHourOfDay()…

Parameters Parameters are special variables Only exist within this function Initialized with value caller passes in: abs(10)  number = 10

Function type return pass answer back to caller Must return right type of data

Function type return OK (but not great) to have more than one return Every path must return

Void Functions Void : nothing Void function returns nothing Just does some work Returns at }

Call Stacks Each function works in a separate stack frame in memory

Scope For Functions Scope of variable/parameter restricted to function it is declared in:

Scope For Functions Only variable available are: Parameters New variables you declare in function

Global Something declared outside any function has global scope Available anywhere in file (after declaration)

Global Uses Way to share information Class rules BAD : side effects No variables at global scope Constants OK

Rules For Functions Communicate with params/return Info to function : parameters Info from function : return value

Rules For Functions Do NOT use cin/cout

Rules For Functions Do NOT use cin/cout Unless job of function is to print or get input

Comparison Return a grade: Print a grade:

Why Functions? Provide abstraction Provide reuse