The Ring programming language version 1.5.1 book - Part 18 of 180
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The document discusses various control structures in Ring including if/elseif/else statements, switch statements, while loops, for loops, and exceptions handling. Examples are provided to demonstrate the syntax and usage of if/elseif/else, switch, while, for, and try/catch structures. Looping constructs like for and while can be used to iterate over a range or list. Logical and short-circuit evaluation rules for conditional expressions are also covered.
![Ring Documentation, Release 1.5.1
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 145](https://image.slidesharecdn.com/171ringfayedringdoc1-171205210859/85/The-Ring-programming-language-version-1-5-1-book-Part-18-of-180-1-320.jpg)
![Ring Documentation, Release 1.5.1
18.7 Exit from two loops
The next example presents how to use the exit command to exit from two loops in one jump.
Example:
for x = 1 to 10
for y = 1 to 10
see "x=" + x + " y=" + y + nl
if x = 3 and y = 5
exit 2 # exit from 2 loops
ok
next
next
18.8 Loop Command
Used to jump to the next iteration in the loop.
Syntax:
loop [expression] # inside loop
Example:
for x = 1 to 10
if x = 3
see "Number Three" + nl
loop
ok
see x + nl
next
18.9 Exit/Loop inside sub functions
While we are inside a loop, we can call a function then use the exit and/or loop command inside that function and the
command will work on the outer loop.
Example:
# print numbers from 1 to 10 except number 5.
for x = 1 to 10
ignore(x,5)
see x + nl
next
func ignore x,y
if x = y
loop
ok
18.7. Exit from two loops 146](https://image.slidesharecdn.com/171ringfayedringdoc1-171205210859/85/The-Ring-programming-language-version-1-5-1-book-Part-18-of-180-2-320.jpg)
![Ring Documentation, Release 1.5.1
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 151](https://image.slidesharecdn.com/171ringfayedringdoc1-171205210859/85/The-Ring-programming-language-version-1-5-1-book-Part-18-of-180-7-320.jpg)
![Ring Documentation, Release 1.5.1
(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 154](https://image.slidesharecdn.com/171ringfayedringdoc1-171205210859/85/The-Ring-programming-language-version-1-5-1-book-Part-18-of-180-10-320.jpg)
The Ring programming language version 1.5.1 book - Part 18 of 180
- 1. Ring Documentation, Release 1.5.1 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 145
- 2. Ring Documentation, Release 1.5.1 18.7 Exit from two loops The next example presents how to use the exit command to exit from two loops in one jump. Example: for x = 1 to 10 for y = 1 to 10 see "x=" + x + " y=" + y + nl if x = 3 and y = 5 exit 2 # exit from 2 loops ok next next 18.8 Loop Command Used to jump to the next iteration in the loop. Syntax: loop [expression] # inside loop Example: for x = 1 to 10 if x = 3 see "Number Three" + nl loop ok see x + nl next 18.9 Exit/Loop inside sub functions While we are inside a loop, we can call a function then use the exit and/or loop command inside that function and the command will work on the outer loop. Example: # print numbers from 1 to 10 except number 5. for x = 1 to 10 ignore(x,5) see x + nl next func ignore x,y if x = y loop ok 18.7. Exit from two loops 146
- 3. Ring Documentation, Release 1.5.1 18.10 Short-circuit evaluation The logical operators and/or follow the short-circuit evaluation. If the first argument of the AND operator is zero, then there is no need to evaluate the second argument and the result will be zero. If the first argument of the OR operator is one, then there is no need to evaluate the second argument and the result will be one. Example: /* output ** nice ** nice ** great */ x = 0 y = 10 if (x = 0 and nice()) and (y = 10 and nice()) see "great" + nl ok func nice see "nice" + nl return 1 Example: # No output x = 0 y = 10 if (x = 1 and nice()) and (y = 10 and nice()) see "great" + nl ok func nice see "nice" + nl return 1 Example: /* output ** nice ** great */ x = 0 y = 10 if (x = 0 and nice()) or (y = 10 and nice()) see "great" + nl ok func nice see "nice" + nl return 1 18.11 Comments about evaluation • True, False, nl & NULL are variables defined by the language • True = 1 18.10. Short-circuit evaluation 147
- 4. Ring Documentation, Release 1.5.1 • 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 18.11. Comments about evaluation 148
- 5. CHAPTER NINETEEN 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. 19.1 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 149
- 6. Ring Documentation, Release 1.5.1 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 150
- 7. Ring Documentation, Release 1.5.1 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 151
- 8. 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") } 152
- 9. Ring Documentation, Release 1.5.1 • 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 153
- 10. Ring Documentation, Release 1.5.1 (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 154