The Ring programming language version 1.7 book - Part 23 of 196
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This document provides information about control structures in Ring including if/elseif/else statements, switch statements, while loops, for loops, and exceptions. It includes syntax examples and explanations of each control structure type. Key points covered include branching with if/elseif/else and switch statements, looping with while, for, and for-in loops, and using try/catch blocks to handle exceptions.
![Ring Documentation, Release 1.7
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
21.3 Exceptions
try
Block of statements
catch
Block of statements
end
21.3. Exceptions 195](https://image.slidesharecdn.com/221pdfsamfayedringdoc1-180710035413/85/The-Ring-programming-language-version-1-7-book-Part-23-of-196-4-320.jpg)
![Ring Documentation, Release 1.7
(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")
}
22.2. Looping 198](https://image.slidesharecdn.com/221pdfsamfayedringdoc1-180710035413/85/The-Ring-programming-language-version-1-7-book-Part-23-of-196-7-320.jpg)
![Ring Documentation, Release 1.7
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
22.3 Exceptions
22.3. Exceptions 199](https://image.slidesharecdn.com/221pdfsamfayedringdoc1-180710035413/85/The-Ring-programming-language-version-1-7-book-Part-23-of-196-8-320.jpg)
The Ring programming language version 1.7 book - Part 23 of 196
- 1. Ring Documentation, Release 1.7 • False = 0 • nl = new line • NULL = empty string = “” • Everything evaluates to true except 0 (False). Example: # output = message from the if statement if 5 # 5 evaluates to true because it's not zero (0). see "message from the if statement" + nl ok 20.11. Comments about evaluation 192
- 2. CHAPTER TWENTYONE CONTROL STRUCTURES - SECOND STYLE In this chapter we are going to learn about the second style of control structures provided by the Ring programming language. 21.1 Branching • If Statement Syntax: if Expression Block of statements elseif Expression Block of statements else Block of statements end Example: put " Main Menu --------- (1) Say Hello (2) About (3) Exit " get nOption if nOption = 1 put "Enter your name : " get name put "Hello " + name + nl elseif nOption = 2 put "Sample : using if statement" + nl elseif nOption = 3 bye else put "bad option..." + nl end • Switch Statement Syntax: switch Expression case Expression Block of statements else Block of statements end 193
- 3. Ring Documentation, Release 1.7 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 21.2 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: 21.2. Looping 194
- 4. Ring Documentation, Release 1.7 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 21.3 Exceptions try Block of statements catch Block of statements end 21.3. Exceptions 195
- 5. CHAPTER TWENTYTWO 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. 22.1 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") } 196
- 6. Ring Documentation, Release 1.7 • 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") } 22.2 Looping • While Loop Syntax: while Expression { Block of statements } Example: Load "stdlib.ring" While True { print(" Main Menu --------- 22.2. Looping 197
- 7. Ring Documentation, Release 1.7 (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") } 22.2. Looping 198
- 8. Ring Documentation, Release 1.7 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 22.3 Exceptions 22.3. Exceptions 199
- 9. Ring Documentation, Release 1.7 try { Block of statements catch Block of statements } 22.3. Exceptions 200
- 10. CHAPTER TWENTYTHREE GETTING INPUT We can get input from the keyboard using • The Give Command • The GetChar() Function • The Input() Function 23.1 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 23.2 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() 201