Introduction to Functions. Functions. Library Functions. Intrinsic Functions. Library Functions. Chapter 6 Fall 2015, CSUS. Chapter 6.

Transcription

1 s Introduction to s Chapter 6 Fall 2015, CSUS Chapter 6.1 Introduction to s Library s 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 Many programming languages come with a collection of pre-defined functions They perform common tasks and save time for the programmer Library s Intrinsic s These are stored in are called "library" functions They are included from a separate file Some languages have built-in "intrinsic" functions These are a core part of the language They are handled directly by the compiler or interpreter

2 Example: Random Numbers Example: Random Numbers A common library function is a Random Number Generator Random numbers are useful for: game programs simulations statistical programs encryption 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 Random Example Random Example Output 9 10 Writing Your Own s Chapter 6.2 Writing Your Own s 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

3 Headers Body 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 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 Body Additional Concerns 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 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 IPO Chart Example IPO Chart Example getprice Input Processing Output Sum Input Processing Output None Prompts the user to enter an item s regular price The item s regular price, as a Real Integer num1 Integer num2 Adds the num1 and num2 to together sum of num1, num

4 Example: Sum Example: Sum returns an integer Integer sum(integer num1, Integer num2) Declare Integer result Set result = num1 + num2 Return result End Return the result Example: Calling Sum 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 Example: Sum Output More Library s Chapter

5 More Library s Flowgorithm Math s The library functions found in each programming language varies The book uses a number of functions in its pseudocode Flowgorithm also contains library functions abs(n) arctan(n) cos(n) int(n) log(n) Absolute Value Trigonometric Arctangent Trigonometric Cosine Integer of a real number Natural Log Flowgorithm Math s Flowgorithm String s log10(n) Log Base 10 len(s) Length of a string sgn(n) sin(n) Mathematical sign Trigonometric Sine char(s, n) Returns a single character from the existing string s. Characters are indexed starting at 0. sqrt(n) Square Root tan(n) Trigonometric Tangent Flowgorithm Type Conversion ToInteger(n) ToReal(n) ToString(n) ToChar(n) ToCode(n) Convert a string to an integer Convert a string to an real Convert a number to a string Convert the character code n to a character Convert a character into a character code 29 5