The Ring programming language version 1.6 book - Part 24 of 189

Ring Documentation, Release 1.6
25.5 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")
}
25.6 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.
25.7 Return Value
The function can return a value using the Return command.
Syntax:
25.5. Main Function 203

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 { }
25.8 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) } }
25.8. Recursion 204

CHAPTER
TWENTYSIX
PROGRAM STRUCTURE
In this chapter we will learn about using many source code files in the same project.
26.1 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.
26.2 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
205

CHAPTER
TWENTYSEVEN
LISTS
In this chapter we are going to learn how to deal with lists.
27.1 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
27.2 Add Items
To add new items to the list, we can use the Add() function.
Syntax:
Add(List,Item)
206

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
27.3 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
27.4 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
27.5 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
27.3. Get List Size 207

27.6 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
27.7 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
27.6. Set List Item 208

27.8 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
27.9 Reverse
We can reverse a list using the reverse() function.
Syntax:
27.8. Sort 209

Reverse(List) ---> Reversed List
Example:
aList = [10,20,30,40,50]
aList = reverse(aList)
see aList # print 50 40 30 20 10
27.10 Insert Items
To insert an item in the list we can use the insert() function.
Syntax:
Insert(List,Index,Item)
The inserted item will be AFTER the Index
Example:
aList = ["A","B","D","E"]
insert(aList,2,"C") # Inserts AFTER Index 2, "C" into Position 3
see aList # print A B C D E
27.11 Nested Lists
The list may contain other lists
Example:
aList = [ 1 , [10,20,30] , 5 , [100,1000,5000] ]
aList2 = [
"one","two",
[3,4],
[20,30], ["three",
"four",
"five",[100,200,300]
]
]
see aList[2] # print 10 20 30
see aList[4][3] + nl # print 5000
see aList2[5][2] + nl # print four
see aList2[5][4][3] # print 300
27.12 Copy Lists
We can copy lists (including nested lists) using the Assignment operator.
Example:
27.10. Insert Items 210

aList = [
"one","two",
[3,4],
[20,30], ["three",
"four",
"five",[100,200,300]
]
]
aList2 = aList # Copy aList to aList2
aList2[5] = "other" # modify item number five
see aList2[5] + nl # print other
see aList[5] # print three four five 100 200 300
27.13 First-class lists
Lists are first-class citizens where we can store lists in variables, pass lists to functions, and return lists from functions.
Example:
aList = duplicate( [1,2,3,4,5] )
see aList[10] + nl # print 5
see mylist() # print 10 20 30 40 50
func duplicate list
nMax = len(list)
for x = 1 to nMax
list + list[x]
next
return list
func mylist return [10,20,30,40,50]
27.14 Using Lists during definition
We can use the list items while we are defining the list for the first time.
Example:
aList = [ [1,2,3,4,5] , aList[1] , aList[1] ]
see aList # print 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
27.15 Passing Lists to Functions
Lists are passed to functions by reference, This means that the called function will work on the same list and can
modify it.
Example:
func main
aList = [1,2,3,4,5] # create list, local in function main
27.13. First-class lists 211

myfunc(aList) # call function, pass list by reference
see aList # print 1 2 3 4 5 6 7 8 9 10
func myfunc list
list + [6,7,8,9,10]
27.16 Access List Items by String Index
Instead of using numbers to determine the item index when we get item value or set item value, We can access items
using string index if the item is a list contains two items and the first item is a string.
Example:
aList = [ ["one",1] , ["two",2] , ["three",3] ]
see aList["one"] + nl +
aList["two"] + nl +
aList["three"] # print 1 2 3
This type of lists can be defined in a better syntax using the : and = operators.
Example:
aList = [ :one = 1 , :two = 2 , :three = 3 ]
see aList["one"] + nl +
aList["two"] + nl +
aList["three"] + nl # print 1 2 3
see aList[1] # print one 1
Tip: using : before identifier (one word) means literal
Note: using = inside list definition create a list of two items where the first item is the left side and the second item is
the right side.
We can add new items to the list using the string index
Example:
aList = []
aList["Egypt"] = "Cairo"
aList["KSA"] = "Riyadh"
see aList["Egypt"] + nl + # print Cairo
aList["KSA"] + nl # print Riyadh
27.17 Passing Parameters Using List
This type of lists is very good for passing parameters to functions Where the order of parameters will not be important
(we can change the order).
Also some parameters maybe optional.
Example:
27.16. Access List Items by String Index 212

The Ring programming language version 1.6 book - Part 24 of 189

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The Ring programming language version 1.6 book - Part 24 of 189