The Ring programming language version 1.5.2 book - Part 21 of 181
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This document provides information about functions and recursion in the Ring programming language. It discusses defining functions, calling functions, declaring parameters, sending parameters, the main function, variable scope, return values, and recursion. Specifically, it explains that Ring supports recursion through functions calling themselves with different parameters, and provides an example of a recursive factorial function.
![CHAPTER
TWENTYFOUR
FUNCTIONS - THIRD STYLE
In this chapter we are going to learn about the next topics :-
• Define functions
• Call functions
• Declare parameters
• Send parameters
• Main Function
• Variables Scope
• Return Value
• Recursion
24.1 Define Functions
To define new function
Syntax:
func <function_name> [parameters] ['{']
Block of statements
['}']
Example:
load "stdlib.ring"
func hello {
print("Hello from function n")
}
24.2 Call Functions
To call function without parameters, we type the function name then ()
Tip: We can call the function before the function definition and the function code.
Example:
176](https://image.slidesharecdn.com/201pdfsamfayedringdoc1-180227021807/85/The-Ring-programming-language-version-1-5-2-book-Part-21-of-181-2-320.jpg)
![Ring Documentation, Release 1.5.2
Return [Expression]
Tip: the Expression after the return command is optional and we can use the return command to end the function
execution without returning any value.
Note: if the function doesn’t return explicit value, it will return NULL (empty string = “” ).
Example:
load "stdlib.ring"
if novalue() = NULL {
print("the function doesn't return a valuen")
}
func novalue { }
24.8 Recursion
The Ring programming language support Recursion and the function can call itself using different parameters.
Example:
load "stdlib.ring"
print( fact(5) ) # output = 120
func fact(x) { if x = 0 { return 1 else return x * fact(x-1) } }
24.8. Recursion 179](https://image.slidesharecdn.com/201pdfsamfayedringdoc1-180227021807/85/The-Ring-programming-language-version-1-5-2-book-Part-21-of-181-5-320.jpg)
![CHAPTER
TWENTYSIX
LISTS
In this chapter we are going to learn how to deal with lists.
26.1 Create Lists
We can create new lists by defining the list items inside square bracts.
Example:
aList = [1,2,3,4,5]
Also we can create new lists using the : operator
Example:
aList = 1:5
aList2 = "a":"z"
Example:
aList = 5:1
aList2 = "z":"a"
Also we can create lists using the list() function
Syntax:
list = list(size)
Example
aList = list(10) # aList contains 10 items
Note: the list index start from 1
26.2 Add Items
To add new items to the list, we can use the Add() function.
Syntax:
Add(List,Item)
181](https://image.slidesharecdn.com/201pdfsamfayedringdoc1-180227021807/85/The-Ring-programming-language-version-1-5-2-book-Part-21-of-181-7-320.jpg)
![Ring Documentation, Release 1.5.2
Example:
aList = ["one","two"]
add(aList,"three")
see aList
Also we can do that using the + operator.
Syntax:
List + item
Example:
aList = 1:10 # create list contains numbers from 1 to 10
aList + 11 # add number 11 to the list
see aList # print the list
26.3 Get List Size
We can get the list size using the len() function
Syntax:
Len(List)
Example:
aList = 1:20 see len(aList) # print 20
26.4 Delete Item From List
To delete an item from the list, we can use the del() function
Syntax:
del(list,index)
Example:
aList = ["one","two","other","three"]
Del(aList,3) # delete item number three
see aList # print one two three
26.5 Get List Item
To get an item from the list, we uses the next syntax
List[Index]
Example:
aList = ["Cairo","Riyadh"]
see "Egypt : " + aList[1] + nl +
"KSA : " + aList[2] + nl
26.3. Get List Size 182](https://image.slidesharecdn.com/201pdfsamfayedringdoc1-180227021807/85/The-Ring-programming-language-version-1-5-2-book-Part-21-of-181-8-320.jpg)
![Ring Documentation, Release 1.5.2
26.6 Set List Item
To set the value of an item inside the list, we can use the next syntax
List[Index] = Expression
Example:
aList = list(3) # create list contains three items
aList[1] = "one" aList[2] = "two" aList[3] = "three"
see aList
26.7 Search
To find an item inside the list we can use the find() function
Syntax:
Find(List,ItemValue) ---> Item Index
Find(List,ItemValue,nColumn) ---> Search in nColumn, returns the Item Index
Find(List,ItemValue,nColumn,cAttribute) ---> Item Index
Example:
aList = ["one","two","three","four","five"]
see find(aList,"three") # print 3
Example:
mylist = [["one",1],
["two",2],
["three",3]]
see find(mylist,"two",1) + nl # print 2
see find(mylist,2,2) + nl # print 2
Also we can use the binarysearch() function to search in sorted list.
Syntax:
BinarySearch(List,ItemValue) ---> Item Index
BinarySearch(List,ItemValue,nColumn) ---> Search in nColumn, returns the Item Index
Example:
aList = ["one","two","three","four","five"]
aList = sort(aList)
see binarysearch(aList,"three")
Output:
five
four
one
three
two
4
26.6. Set List Item 183](https://image.slidesharecdn.com/201pdfsamfayedringdoc1-180227021807/85/The-Ring-programming-language-version-1-5-2-book-Part-21-of-181-9-320.jpg)
![Ring Documentation, Release 1.5.2
26.8 Sort
We can sort the list using the sort() function.
Syntax:
Sort(List) ---> Sorted List
Sort(List,nColumn) ---> Sorted List based on nColumn
Sort(List,nColumn,cAttribute) ---> Sorted List based on Object Attribute
Example:
aList = [10,12,3,5,31,15]
aList = sort(aList) see aList # print 3 5 10 12 15 31
We can sort list of strings
Example:
mylist = ["mahmoud","samir","ahmed","ibrahim","mohammed"]
see mylist # print list before sorting
mylist = sort(mylist) # sort list
see "list after sort"+nl
see mylist # print ahmed ibrahim mahmoud mohammed samir
We can sort a list based on a specific column.
Example:
aList = [ ["mahmoud",15000] ,
["ahmed", 14000 ] ,
["samir", 16000 ] ,
["mohammed", 12000 ] ,
["ibrahim",11000 ] ]
aList2 = sort(aList,1)
see aList2
Output:
ahmed
14000
ibrahim
11000
mahmoud
15000
mohammed
12000
samir
16000
26.9 Reverse
We can reverse a list using the reverse() function.
Syntax:
26.8. Sort 184](https://image.slidesharecdn.com/201pdfsamfayedringdoc1-180227021807/85/The-Ring-programming-language-version-1-5-2-book-Part-21-of-181-10-320.jpg)
The Ring programming language version 1.5.2 book - Part 21 of 181
- 1. Ring Documentation, Release 1.5.2 if novalue() = NULL put "the function doesn't return a value" + nl end def novalue 23.8 Recursion The Ring programming language support Recursion and the function can call itself using different parameters. Example: put fact(5) # output = 120 def fact x if x = 0 return 1 else return x * fact(x-1) end 23.8. Recursion 175
- 2. CHAPTER TWENTYFOUR FUNCTIONS - THIRD STYLE In this chapter we are going to learn about the next topics :- • Define functions • Call functions • Declare parameters • Send parameters • Main Function • Variables Scope • Return Value • Recursion 24.1 Define Functions To define new function Syntax: func <function_name> [parameters] ['{'] Block of statements ['}'] Example: load "stdlib.ring" func hello { print("Hello from function n") } 24.2 Call Functions To call function without parameters, we type the function name then () Tip: We can call the function before the function definition and the function code. Example: 176
- 3. Ring Documentation, Release 1.5.2 load "stdlib.ring" hello() func hello { print("Hello from function n") } Example: load "stdlib.ring" first() second() func first { print("message from the first function n") } func second { print("message from the second function n") } 24.3 Declare parameters To declare the function parameters, after the function name type the list of parameters as a group of identifiers separated by comma. Example: load "stdlib.ring" func sum(x,y) { print(x+y) } 24.4 Send Parameters To send parameters to function, type the parameters inside () after the function name Syntax: funcname(parameters) Example: /* output ** 8 ** 3000 */ load "stdlib.ring" sum(3,5) sum(1000,2000) func sum(x,y) { print(x+y) } 24.3. Declare parameters 177
- 4. Ring Documentation, Release 1.5.2 24.5 Main Function Using the Ring programming language, the Main Function is optional, when it’s defined, it will be executed after the end of other statements. if no other statements comes alone, the main function will be the first entry point Example: # this program will print the hello world message first then execute the main function load "stdlib.ring" print("Hello, World! n") func main { print("Message from the main function n") } 24.6 Variables Scope The Ring programming language uses lexical scoping to determine the scope of a variable. Variables defined inside functions (including function parameters) are local variables. Variables defined outside func- tions (before any function) are global variables. Inside any function we can access the variables defined inside this function beside the global variables. Example: # the program will print numbers from 10 to 1 load "stdlib.ring" x = 10 # x is a global variable. func main { for t = 1 to 10 { # t is a local variable mycounter() # call function } } func mycounter { print("#{x}n") # print the global variable value x-- # decrement } Note: Using the main function before the for loop declare the t variable as a local variable, It’s recommended to use the main functions instead of typing the instructions directly to set the scope of the new variables to local. 24.7 Return Value The function can return a value using the Return command. Syntax: 24.5. Main Function 178
- 5. Ring Documentation, Release 1.5.2 Return [Expression] Tip: the Expression after the return command is optional and we can use the return command to end the function execution without returning any value. Note: if the function doesn’t return explicit value, it will return NULL (empty string = “” ). Example: load "stdlib.ring" if novalue() = NULL { print("the function doesn't return a valuen") } func novalue { } 24.8 Recursion The Ring programming language support Recursion and the function can call itself using different parameters. Example: load "stdlib.ring" print( fact(5) ) # output = 120 func fact(x) { if x = 0 { return 1 else return x * fact(x-1) } } 24.8. Recursion 179
- 6. CHAPTER TWENTYFIVE PROGRAM STRUCTURE In this chapter we will learn about using many source code files in the same project. 25.1 Source Code File Sections Each source code file may contains the next sections (in the same order). Source Code File Sections Load Files Statements and Global Variables Functions Packages and Classes The application maybe one or more of files. 25.2 Using Many Source Code Files To include another source file in the project, just use the load command. Syntax: Load "filename.ring" Note: The Load command is executed directly by the compiler in the parsing stage Tip: if you don’t know the file name until the runtime, or you need to use functions to get the file path, just use eval(). Example: # File : Start.ring Load "sub.ring" sayhello("Mahmoud") # File : sub.ring func sayhello cName see "Hello " + cName + nl 180
- 7. CHAPTER TWENTYSIX LISTS In this chapter we are going to learn how to deal with lists. 26.1 Create Lists We can create new lists by defining the list items inside square bracts. Example: aList = [1,2,3,4,5] Also we can create new lists using the : operator Example: aList = 1:5 aList2 = "a":"z" Example: aList = 5:1 aList2 = "z":"a" Also we can create lists using the list() function Syntax: list = list(size) Example aList = list(10) # aList contains 10 items Note: the list index start from 1 26.2 Add Items To add new items to the list, we can use the Add() function. Syntax: Add(List,Item) 181
- 8. Ring Documentation, Release 1.5.2 Example: aList = ["one","two"] add(aList,"three") see aList Also we can do that using the + operator. Syntax: List + item Example: aList = 1:10 # create list contains numbers from 1 to 10 aList + 11 # add number 11 to the list see aList # print the list 26.3 Get List Size We can get the list size using the len() function Syntax: Len(List) Example: aList = 1:20 see len(aList) # print 20 26.4 Delete Item From List To delete an item from the list, we can use the del() function Syntax: del(list,index) Example: aList = ["one","two","other","three"] Del(aList,3) # delete item number three see aList # print one two three 26.5 Get List Item To get an item from the list, we uses the next syntax List[Index] Example: aList = ["Cairo","Riyadh"] see "Egypt : " + aList[1] + nl + "KSA : " + aList[2] + nl 26.3. Get List Size 182
- 9. Ring Documentation, Release 1.5.2 26.6 Set List Item To set the value of an item inside the list, we can use the next syntax List[Index] = Expression Example: aList = list(3) # create list contains three items aList[1] = "one" aList[2] = "two" aList[3] = "three" see aList 26.7 Search To find an item inside the list we can use the find() function Syntax: Find(List,ItemValue) ---> Item Index Find(List,ItemValue,nColumn) ---> Search in nColumn, returns the Item Index Find(List,ItemValue,nColumn,cAttribute) ---> Item Index Example: aList = ["one","two","three","four","five"] see find(aList,"three") # print 3 Example: mylist = [["one",1], ["two",2], ["three",3]] see find(mylist,"two",1) + nl # print 2 see find(mylist,2,2) + nl # print 2 Also we can use the binarysearch() function to search in sorted list. Syntax: BinarySearch(List,ItemValue) ---> Item Index BinarySearch(List,ItemValue,nColumn) ---> Search in nColumn, returns the Item Index Example: aList = ["one","two","three","four","five"] aList = sort(aList) see binarysearch(aList,"three") Output: five four one three two 4 26.6. Set List Item 183
- 10. Ring Documentation, Release 1.5.2 26.8 Sort We can sort the list using the sort() function. Syntax: Sort(List) ---> Sorted List Sort(List,nColumn) ---> Sorted List based on nColumn Sort(List,nColumn,cAttribute) ---> Sorted List based on Object Attribute Example: aList = [10,12,3,5,31,15] aList = sort(aList) see aList # print 3 5 10 12 15 31 We can sort list of strings Example: mylist = ["mahmoud","samir","ahmed","ibrahim","mohammed"] see mylist # print list before sorting mylist = sort(mylist) # sort list see "list after sort"+nl see mylist # print ahmed ibrahim mahmoud mohammed samir We can sort a list based on a specific column. Example: aList = [ ["mahmoud",15000] , ["ahmed", 14000 ] , ["samir", 16000 ] , ["mohammed", 12000 ] , ["ibrahim",11000 ] ] aList2 = sort(aList,1) see aList2 Output: ahmed 14000 ibrahim 11000 mahmoud 15000 mohammed 12000 samir 16000 26.9 Reverse We can reverse a list using the reverse() function. Syntax: 26.8. Sort 184