Functions

1
Functions
2
Quick Review

• What is a Function?
• A module of code that performs a specific job.
• Examples
• Function that determines the maximum of two
  numbers.
• Function that sorts a list of names.

3
Boss Analogy

• One function can delegate certain jobs to
  specific functions.

Boss Function
Max Function
Sort Function
4
Important Concept 1

• Divide and Conquer break large programs into a
  series of smaller functions.
• Helps manage complexity.
• Makes it easier to build large programs.
• Makes is easier to debug programs.

5
Important Concept 2

• Abstraction most of the time, you need to know
  what a function does, but not how it actually
  does it.
• Also helps manage complexity.
• You can use other peoples code, without
  understanding how it works.

6
Using Pre-Packaged Functions

• Standard C includes lots of pre-packaged
  libraries
• ctype.h character manipulation
• math.h mathematical functions
• stdio.h standard input/output
• stdlib.h random numbers, memory handling
• string.h string manipulation
• time.h date/time functions
• All of these are detailed in the Book.

7
Function Concepts

• Function Prototype
• Function Definition
• Function Call

8
Function Prototype

• Tells you what type of data the function is
  expecting, and what type of data the function
  returns.
• Represents a communication protocol that enables
  two functions to talk.
• If you want to use a pre-built function, you need
  to learn to read prototypes.

9
sqrt Function

• double sqrt (double)
• This function therefore accepts one double value,
  and returns one double value.

Return data type
Function argument data type
10
Using sqrt()

• include ltstdio.hgt
• include ltmath.hgt
• main ()
• double value
• value sqrt(9.0)/function call/
• printf ("f", value)

11
Creating your own Functions
12
Creating your own Functions

• include ltstdio.hgt
• int square(int)
• main ()
• printf("d ", square(5))
• int square(int y)
• return y y

Function Prototype must be declared at top of
program.
Function Call invokes the function
Function Definition contains the actual
function code.
Returns a value back up to main.
13
Understanding the Program
Main Function
Take this Integer!
Heres the answer. Its an integer!
Square function
14
Function Template

• Use this template for adding functions to your
  program.
• return-value-type function-name (parameter-list)
• return-value-type function-name (parameter-list)
• variable declarations
• statements of work
• return statement (optional outside of this
  class)

Function Prototype must be declared at top of
program.
Function Definition contains the actual
function code.