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.

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 statement\n")
elseif nOption = 3
        bye
else
        print("bad option...\n")
}

• 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 statement\n")
case 3
        Bye
else
        print("bad option...\n")
}

Looping

• While Loop

Syntax:

while Expression {
        Block of statements
}

Example:

Load "stdlib.ring"

While True {

        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 statement\n")
        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")
}

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

Exceptions

try {
        Block of statements
catch
        Block of statements
}