Control Structures - First Style¶
In this chapter we are going to learn about the control structures provided by the Ring programming language.
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
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
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:
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
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
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
Do Again Loop¶
Syntax:
do Block of statements again expression
Example:
x = 1 do see x + nl x++ again x <= 10
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
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
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
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
Comments about evaluation¶
True, False, nl & NULL are variables defined by the language
True = 1
False = 0
nl = new line
NULL = empty string = ""
Everything evaluates to true except 0 (False).
Example: