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 nStart = 0+nStart See "End : " give nEnd nEnd = 0+nEnd See "Step : " give nStep nStep = 0+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|foreach 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 Note
We can use the ForEach keyword instead of the For keyword
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), NULL (Empty String), Empty List and Lists that wrap C pointer where the pointer value is NULL.
Example: