The Ring programming language version 1.5.3 book - Part 20 of 184

1. Ring Documentation, Release 1.5.3
Example:
Put "
Main Menu
---------
(1) Say Hello
(2) About
(3) Exit
" Get nOption
Switch nOption
Case 1 Put "Enter your name : " Get name Put "Hello " + name + nl
Case 2 Put "Sample : using switch statement" + nl
Case 3 Bye
Else Put "bad option..." + nl
End
19.2 Looping
• While Loop
Syntax:
while Expression
Block of statements
end
Example:
While True
Put "
Main Menu
---------
(1) Say Hello
(2) About
(3) Exit
" Get nOption
Switch nOption
Case 1
Put "Enter your name : "
Get name
Put "Hello " + name + nl
Case 2
Put "Sample : using while loop" + nl
Case 3
Bye
Else
Put "bad option..." + nl
End
End
• For Loop
Syntax:
19.2. Looping 165

2. Ring Documentation, Release 1.5.3
for identifier=expression to expression [step expression]
Block of statements
end
Example:
# print numbers from 1 to 10
for x = 1 to 10 put x + nl end
Example:
# Dynamic loop
Put "Start : " get nStart
Put "End : " get nEnd
Put "Step : " get nStep
For x = nStart to nEnd Step nStep
Put x + nl
End
Example:
# print even numbers from 0 to 10
for x = 0 to 10 step 2
Put x + nl
end
Example:
# print even numbers from 10 to 0
for x = 10 to 0 step -2
put x + nl
end
• For in Loop
Syntax:
for identifier in List/String [step expression]
Block of statements
end
Example:
aList = 1:10 # create list contains numbers from 1 to 10
for x in aList put x + nl end # print numbers from 1 to 10
19.3 Exceptions
try
Block of statements
catch
Block of statements
end
19.3. Exceptions 166

3. CHAPTER
TWENTY
CONTROL STRUCTURES - THIRD STYLE
In this chapter we are going to learn about the third style of control structures provided by the Ring programming
language.
20.1 Branching
• If Statement
Syntax:
if Expression {
Block of statements
elseif Expression
Block of statements
else
Block of statements
}
Example:
Load "stdlib.ring"
print("
Main Menu
---------
(1) Say Hello
(2) About
(3) Exit
")
nOption = getnumber()
if nOption = 1 {
print("Enter your name : ")
name = getstring()
print("Hello #{name}n")
elseif nOption = 2
print("Sample : using if statementn")
elseif nOption = 3
bye
else
print("bad option...n")
}
167

4. Ring Documentation, Release 1.5.3
• Switch Statement
Syntax:
switch Expression {
case Expression
Block of statements
else
Block of statements
}
Example:
Load "stdlib.ring"
print("
Main Menu
---------
(1) Say Hello
(2) About
(3) Exit
")
nOption = GetString()
switch nOption {
case 1
print("Enter your name : ")
name = getstring()
print("Hello #{name}n")
case 2
print("Sample : using switch statementn")
case 3
Bye
else
print("bad option...n")
}
20.2 Looping
• While Loop
Syntax:
while Expression {
Block of statements
}
Example:
Load "stdlib.ring"
While True {
print("
Main Menu
---------
20.2. Looping 168

5. Ring Documentation, Release 1.5.3
(1) Say Hello
(2) About
(3) Exit
")
nOption = GetString()
switch nOption {
case 1
print("Enter your name : ")
name = getstring()
print("Hello #{name}n")
case 2
print("Sample : using switch statementn")
case 3
Bye
else
print("bad option...n")
}
}
• For Loop
Syntax:
for identifier=expression to expression [step expression] {
Block of statements
}
Example:
# print numbers from 1 to 10
load "stdlib.ring"
for x = 1 to 10 {
print("#{x}n")
}
Example:
load "stdlib.ring"
# Dynamic loop
print("Start : ") nStart = getnumber()
print("End : ") nEnd = getnumber()
print("Step : ") nStep = getnumber()
for x = nStart to nEnd step nStep {
print("#{x}n")
}
Example:
load "stdlib.ring"
# print even numbers from 0 to 10
for x = 0 to 10 step 2 {
print("#{x}n")
}
20.2. Looping 169

6. Ring Documentation, Release 1.5.3
Example:
load "stdlib.ring"
# print even numbers from 10 to 0
for x = 10 to 0 step -2 {
print("#{x}n")
}
• For in Loop
Syntax:
for identifier in List/String [step expression] {
Block of statements
}
Example:
load "stdlib.ring"
aList = 1:10 # create list contains numbers from 1 to 10
for x in aList { print("#{x}n") } # print numbers from 1 to 10
Example:
load "stdlib.ring"
aList = 1:10 # create list contains numbers from 1 to 10
# print odd items inside the list
for x in aList step 2 {
print("#{x}n")
}
When we use (For in) we get items by reference.
This means that we can read/edit items inside the loop.
Example:
load "stdlib.ring"
aList = 1:5 # create list contains numbers from 1 to 5
# replace list numbers with strings
for x in aList {
switch x {
case 1 x = "one"
case 2 x = "two"
case 3 x = "three"
case 4 x = "four"
case 5 x = "five"
}
}
print(aList) # print the list items
20.3 Exceptions
20.3. Exceptions 170

7. Ring Documentation, Release 1.5.3
try {
Block of statements
catch
Block of statements
}
20.3. Exceptions 171

8. CHAPTER
TWENTYONE
GETTING INPUT
We can get input from the keyboard using
• The Give Command
• The GetChar() Function
• The Input() Function
21.1 Give Command
Syntax:
Give VariableName
Example:
See "Enter the first number : " Give nNum1
See "Enter the second number : " Give nNum2
See "Sum : " + ( 0 + nNum1 + nNum2 )
Output:
Enter the first number : 3
Enter the second number : 4
Sum : 7
21.2 GetChar() Function
We can get one character from the standard input using the GetChar() function
Syntax:
GetChar() ---> Character
Example:
While True
See "
Main Menu
(1) Say Hello
(2) Exit
"
Option = GetChar()
172

9. Ring Documentation, Release 1.5.3
GetChar() GetChar() # End of line
# the previous two lines can be replaced with the next line
# Give Option
if Option = 1
see "Enter your name : " give cName
see "Hello " + cName
else
bye
ok
End
21.3 Input() Function
We can get input from the keyboard using the Input() function
Syntax:
Input(nCount) ---> string
The function will wait until nCount characters (at least) are read
Example:
See "Enter message (30 characters) : " cMsg = input(30)
See "Message : " + cMsg
21.3. Input() Function 173

10. CHAPTER
TWENTYTWO
FUNCTIONS - FIRST 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
22.1 Define Functions
To define new function
Syntax:
func <function_name> [parameters]
Block of statements
Note: No keyword is required to end the function definition.
Example:
func hello
see "Hello from function" + nl
22.2 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:
174