The Ring programming language version 1.5.2 book - Part 18 of 181

1. Ring Documentation, Release 1.5.2
15.6 Using Emacs Editor
Folder : ring/editor/emacs
Check the ReadMe file for installation instructions.
Screen Shot:
15.6. Using Emacs Editor 145

2. CHAPTER
SIXTEEN
VARIABLES
To create a new variable, you just need to determine the variable name & value. The value will determine the variable
type and you can change the value to switch between the types using the same variable name.
Syntax:
<Variable Name> = <Value>
Tip: The operator ‘=’ is used here as an Assignment operator and the same operator can be used in conditions, but
for testing equality of expressions.
Note: The Variable will contains the real value (not a reference). This means that once you change the variable value,
the old value will be removed from memory (even if the variable contains a list or object).
16.1 Dynamic Typing
Ring is a dynamic programming language that uses Dynamic Typing.
x = "Hello" # x is a string
see x + nl
x = 5 # x is a number (int)
see x + nl
x = 1.2 # x is a number (double)
see x + nl
x = [1,2,3,4] # x is a list
see x # print list items
x = date() # x is a string contains date
see x + nl
x = time() # x is a string contains time
see x + nl
x = true # x is a number (logical value = 1)
see x + nl
x = false # x is a number (logical value = 0)
see x + nl
16.2 Deep Copy
We can use the assignment operator ‘=’ to copy variables. We can do that to copy values like strings & numbers. Also,
we can copy complete lists & objects. The assignment operator will do a complete duplication for us. This operation
called Deep Copy
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list = [1,2,3,"four","five"]
list2 = list
list = []
See list # print the first list - no items to print
See "********" + nl
See list2 # print the second list - contains 5 items
16.3 Weakly Typed
Ring is a weakly typed language, this means that the language can automatically convert between data types (like
string & numbers) when that conversion make sense.
Rules:
<NUMBER> + <STRING> --> <NUMBER>
<STRING> + <NUMBER> --> <STRING>
Note: The same operator ‘+’ can be used as an arithmetic operator or for string concatenation.
Example:
x = 10 # x is a number
y = "20" # y is a string
sum = x + y # sum is a number (y will be converted to a number)
Msg = "Sum = " + sum # Msg is a string (sum will be converted to a string)
see Msg + nl
16.3. Weakly Typed 147

4. CHAPTER
SEVENTEEN
OPERATORS
In this chapter we will introduce the operators provided by the Ring programming langauge.
17.1 Arithmetic Operators
The next table presents all of the arithmetic operators provided by the Ring language. Assume variable X=50 and
variable Y=10 then:
Operator Description Example Result
+ Add x+y 60
- Subtract x-y 40
* Multiplies x*y 500
/ Divide x/y 5
% Modulus x%y 0
++ Increment x++ 51
- - Decrement x- - 49
17.2 Relational Operators
The next table presents all of the relational operators provided by the Ring language. Assume variable X=50 and
variable Y=10 then:
Operator Description Example Result
= Equal x = y False
!= Not Equal x != y True
> Greater than x > y True
< Less than x < y False
>= Greater or Equal x >= y True
<= Less than or Equal x <= y False
17.3 Logical Operators
The next table presents all of the logical operators provided by the Ring language. Assume variable X=True and
variable Y=False then:
Operator Description Example Result
and Logical AND x and y False
or Logical OR x or y True
not Logical Not not x False
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17.4 Bitwise Operators
The next table presents all of the bitwise operators provided by the Ring language. Assume variable X=8 and variable
Y=2 then:
Operator Description Example Result
& Binary AND x & y 0
| Binary OR x | y 10
^ Binary XOR x ^ y 10
~ Binary Ones Complement ~x -9
<< Binary Left Shift x << y 32
>> Binary Right Shift x >> y 2
17.5 Assignment Operators
The next table presents all of the assignment operators provided by the Ring language.
Assume variable X=8 then:
Operator Description Example Result
= Assignment x = 10 x=10
+= Add AND assignment x += 5 x=13
-= Subtract AND assignment x -= 3 x=5
*= Multiply AND assignment x *= 2 x=16
/= Divide AND assignment x /= 3 x=2.67
%= Modulus AND assignment x %= 2 x=0
<<= Left shift AND assignment x <<= 2 x=32
>>= Right shift AND assignment x >>= 2 x=2
&= Bitwise AND assignment x &= 4 x=0
|= Bitwise OR and assignment x |= 3 x=11
^= Bitwise XOR and assignment x ^= 4 x=12
17.6 Misc Operators
Operator Description
:literal using : before identifier mean literal
Start:End create list contains items from start to end
[list items] define list items
list[index] access list item
obj.name using the dot operator to access object members (attributes/methods).
obj {stmts} execute statements with direct access to object attributes & methods
func(para,...) call function using parameters separated by comma
17.7 Operators Precedence
The next table present operators from higher precedence (Evaluated first) to lower precedence.
17.4. Bitwise Operators 149

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Operator
. [] () {}
- ~ :Literal [list items]
++ - -
Start:End
* / %
+ -
<< >>
&
| ^
< > <= >=
= !=
not
and or
Assignment = += -= *= /= %=>>= <<= &= ^= |=
Example:
See 3+5*4 # prints 23
17.7. Operators Precedence 150

7. CHAPTER
EIGHTEEN
CONTROL STRUCTURES - FIRST STYLE
In this chapter we are going to learn about the control structures provided by the Ring programming language.
18.1 Branching
• If Statement
Syntax:
if Expression
Block of statements
but Expression
Block of statements
else
Block of statements
ok
Example:
see "
Main Menu
---------
(1) Say Hello
(2) About
(3) Exit
" give nOption
if nOption = 1 see "Enter your name : " give name see "Hello " + name + nl
but nOption = 2 see "Sample : using if statement" + nl
but nOption = 3 bye
else see "bad option..." + nl
ok
• Switch Statement
Syntax:
switch Expression
on Expression
Block of statements
other
Block of statements
off
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Example:
See "
Main Menu
---------
(1) Say Hello
(2) About
(3) Exit
" Give nOption
Switch nOption
On 1 See "Enter your name : " Give name See "Hello " + name + nl
On 2 See "Sample : using switch statement" + nl
On 3 Bye
Other See "bad option..." + nl
Off
18.2 Looping
• While Loop
Syntax:
while Expression
Block of statements
end
Example:
While True
See "
Main Menu
---------
(1) Say Hello
(2) About
(3) Exit
" Give nOption
Switch nOption
On 1
See "Enter your name : "
Give name
See "Hello " + name + nl
On 2
See "Sample : using while loop" + nl
On 3
Bye
Other
See "bad option..." + nl
Off
End
• For Loop
Syntax:
18.2. Looping 152

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for identifier=expression to expression [step expression]
Block of statements
next
Example:
# print numbers from 1 to 10
for x = 1 to 10 see x + nl next
Example:
# Dynamic loop
See "Start : " give nStart
See "End : " give nEnd
See "Step : " give nStep
For x = nStart to nEnd Step nStep
see x + nl
Next
Example:
# print even numbers from 0 to 10
for x = 0 to 10 step 2
see x + nl
next
Example:
# print even numbers from 10 to 0
for x = 10 to 0 step -2
see x + nl
next
• For in Loop
Syntax:
for identifier in List/String [step expression]
Block of statements
next
Example:
aList = 1:10 # create list contains numbers from 1 to 10
for x in aList see x + nl next # print numbers from 1 to 10
18.3 Using The Step option with For in
We can use the Step option with For in to skip number of items in each iteration
Example:
aList = 1:10 # create list contains numbers from 1 to 10
# print odd items inside the list
for x in aList step 2
see x + nl
next
18.3. Using The Step option with For in 153

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18.4 Using For in to modify lists
When we use (For in) we get items by reference.
This means that we can read/edit items inside the loop.
Example:
aList = 1:5 # create list contains numbers from 1 to 5
# replace list numbers with strings
for x in aList
switch x
on 1 x = "one"
on 2 x = "two"
on 3 x = "three"
on 4 x = "four"
on 5 x = "five"
off
next
see aList # print the list items
18.5 Do Again Loop
Syntax:
do
Block of statements
again expression
Example:
x = 1
do
see x + nl
x++
again x <= 10
18.6 Exit Command
Used to go outside one or more of loops.
Syntax:
exit [expression] # inside loop
Example:
for x = 1 to 10
see x + nl
if x = 5 exit ok
next
18.4. Using For in to modify lists 154