Programming - IT - Software Design

CHAPTER 6

Functions

Chapter Topics 6.1 Introduction to Functions: 


Generating Random Numbers 6.2 Writing Your Own Functions 6.3 More Library Functions

6.1 Introduction to Functions A function is a module that returns a value back

to the part of the program that called it – Many languages provide libraries of functions that

you can use, such as Random Number Generator – A function is like a module, but it returns a value

that can be used in your program Library functions

– Written functions that come with most languages – Usually common tasks that save time for the

programmer because it allows for code reuse

6.1 Introduction to Functions The Random Number Generator function is useful in:

– Game programs – Simulation programs – Statistical programs – Computer security such as encryption

How random function works – Set number = random(1, 100) – 1 and 100 define the range of the number that can be

returned, and are called arguments – The function is called and a random number is returned and

assigned to the variable number

6.2 Writing Your Own Functions Most languages allow coders to write functions • The function header specifies the data type of

the value that is returned, the name of the function, and any parameter variables

• The function body are the statements that execute when the function is called

• The return statement specifies the value that is returned when the function ends

6.2 Writing Your Own Functions

6.2 Writing Your Own Functions

Additional concerns – While you can pass as many arguments into a function,

you can only return one value – Functions simplify code, increase the speed of

development, and ease the facilitation of teamwork – Each function should be flowcharted separately – IPO (input, processing, and output), can be used to show

what a function does

IPO Chart for the getRegularPrice Function Input Processing Output

None Prompts the user to enter an item’s regular price

The item’s regular price, as a Real

6.3 More Library Functions Mathematical Functions

– Functions typically accept one or more values as arguments, perform a mathematical operation using the arguments, and return the results

Set result = sqrt(16) – Returns the square root of 16

Set area = power(4, 2) – Raises the value of 4 to the power of 2

6.3 More Library Functions Other Common Mathematical Functions

– abs calculates the absolute value of a number – cos returns the cosine of an argument – round rounds to the nearest integer – sin returns the sine of an argument – tan returns the tangent of an argument

6.3 More Library Functions Data Type Conversion Functions

– Library functions that convert values from one data type to another • toInteger converts a real to an integer • toReal converts an integer to a real

– Real numbers can store integers – Integers cannot store real numbers – Type mismatch errors will occur without

converting values

6.3 More Library Functions Formatting Functions

– Allow to format a number in a certain way – currencyFormat will be used to format a number

to a currency Declare Real amount = 6450.879 Display currencyFormat(amount) – Display would be $6,450.88

6.3 More Library Functions String Functions

– Allow for working with strings – length function returns the length of a function – append function joins multiple strings together – toUpper and toLower converts a string to

upper or lower case – substring can extract a character or a portion

of a string out of a string

6.3 More Library Functions String Functions

– contains identifies similar strings within two strings

– stringToInteger and stringToReal converts string that stores a number, to a number data type

– isInteger and isReal test numbers to see if it can be converted to a string