The Ring programming language version 1.9 book - Part 28 of 210

1. CHAPTER
TWENTYSEVEN
FUNCTIONS - SECOND 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
27.1 Define Functions
To define new function
Syntax:
def <function_name> [parameters]
Block of statements
[end]
Note: the keyword ‘end’ is optional.
Example:
def hello
put "Hello from function" + nl
end
27.2 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:
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hello()
def hello
put "Hello from function" + nl
end
Example:
first() second()
def first put "message from the first function" + nl
def second put "message from the second function" + nl
27.3 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:
def sum x,y
put x+y+nl
end
27.4 Send Parameters
To send parameters to function, type the parameters inside () after the function name
Syntax:
funcname(parameters)
Example:
/* output
** 8
** 3000
*/
sum(3,5) sum(1000,2000)
def sum x,y put x+y+nl
27.5 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:
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# this program will print the hello world message first then execute the main function
put "Hello World!" + nl
def main
put "Message from the main function" + nl
end
27.6 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
x = 10 # x is a global variable.
def main
for t = 1 to 10 # t is a local variable
mycounter() # call function
end
end
def mycounter
put x + nl # print the global variable value
x-- # decrement
end
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.
27.7 Return Value
The function can return a value using the Return command.
Syntax:
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:
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if novalue() = NULL
put "the function doesn't return a value" + nl
end
def novalue
27.8 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
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5. CHAPTER
TWENTYEIGHT
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
28.1 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")
}
28.2 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:
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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") }
28.3 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)
}
28.4 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) }
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28.5 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")
}
28.6 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.
28.7 Return Value
The function can return a value using the Return command.
Syntax:
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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 { }
28.8 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) } }
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9. CHAPTER
TWENTYNINE
PROGRAM STRUCTURE
In this chapter we will learn about using many source code files in the same project.
29.1 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.
29.2 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
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29.3 Load Package
Using the ‘load’ command we can use many ring source files in the same project
But all of these files will share the same global scope
We have also the “Load Package” command
Using “Load Package” we can load a library (*.ring file) in new global scope
This is very useful to create libraries that avoid conflicts in global variables
Example:
File: loadpackage.ring
x = 100
? "Hello, World!"
load package "testloadpackage.ring"
? x
test()
File: testloadpackage.ring
? "Hello from testloadpackage.ring"
x = 1000
test()
func test
? x
Output:
Hello, World!
Hello from testloadpackage.ring
1000
100
1000
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