A function is a module that returns a value back to the part of the program that called it Found in practically all programming languages 10/28/2016
Sacramento State - CSc 10A
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Library Functions
Many programming languages come with a collection of pre-defined functions They perform common tasks and save time for the programmer 10/28/2016
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Library Functions
These are stored in are called "library" functions They are included from a separate file
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Intrinsic Functions
Some languages have built-in "intrinsic" functions These are a core part of the language They are handled directly by the compiler or interpreter 10/28/2016
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Example: Random Numbers A common library function is a Random Number Generator Random numbers are useful for: • • • • 10/28/2016
game programs simulations statistical programs encryption Sacramento State - CSc 10A
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Example: Random Numbers
The function returns a random number either between two integers Generally accepts 1 or 2 arguments: • Random(n) – random between 0 and n-1 • Random(n, m) – random between n and m
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Random Example
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Random Example Output
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Writing Your Own Functions Chapter 6.2
Writing Your Own Functions Most languages allow programmers to write their own functions They can be called and used just like any library function Most programmers create their own library 10/28/2016
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Function Headers
The function header specifies information about the function itself It contains: • name of the function • any parameter variables • data type of the value that is returned
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Function Body
The function body contains the statements that execute when the function calls At the end of the body, a return statement specifies the value that is returned when the function ends
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Function Body
Some program languages allow a return statement to be located anywhere However, it is considered good style to have a one-way-in-one-way-out design So, ideally, there is only one return statement – and it is the last statement 10/28/2016
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Additional Concerns Each function should be flowcharted separately To graphically represent a function's treatment of data, we can use an IPO (input, processing, and output) chart The IPO contains the arguments, output type, and a description of the behavior 10/28/2016
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IPO Chart Example getPrice Function Input None
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Processing Prompts the user to enter an item’s regular price
Output The item’s regular price, as a Real
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IPO Chart Example Sum Function Input Integer num1 Integer num2
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Processing Adds the num1 and num2 to together
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Output sum of num1, num2
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Example: Sum Function returns an integer
Function Integer sum(Integer num1, Integer num2) Declare Integer result Set result = num1 + num2 Return result End Function Return the result 10/28/2016
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Example: Sum
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Example: Calling Sum
Module Main Declare Integer x Declare Integer y Input x Input y
Output the result of the function
Display sum(x, y) End Module
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Example: Calling Sum
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Example: Sum Output
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More Library Functions
Chapter 6.3
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More Library Functions The library functions found in each programming language varies The book uses a number of functions in its pseudocode Flowgorithm also contains library functions 10/28/2016
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Flowgorithm Math Functions Function
Description
abs(n)
Absolute Value
arctan(n)
Trigonometric Arctangent
cos(n)
Trigonometric Cosine
int(n)
Integer of a real number
log(n)
Natural Log
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Flowgorithm Math Functions Function
Description
log10(n)
Log Base 10
sgn(n)
Mathematical sign
sin(n)
Trigonometric Sine
sqrt(n)
Square Root
tan(n)
Trigonometric Tangent
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Flowgorithm String Functions Function
Description
len(s)
Length of a string
char(s, n)
Returns a single character from the existing string s. Characters are indexed starting at 0.
