Table of Contents
Ruby is one of the programming languages you can use almost everywhere. It is also simple and very easy to learn. This makes it a very good choice if you want to learn new programming language, especially if it is your first programming language. Will you give Ruby a chance? If so, you are on the right place. This series will teach you all you need to learn this programming language.
Getting Started With Ruby the Easy Way Part 1 (Comments, Variables, Strings).
Getting Started With Ruby the Easy Way Part 2 (Data Types Pt1).
Getting Started With Ruby the Easy Way Part 3 (Data Types Pt2, Control Flow Pt1).
Getting Started With Ruby the Easy Way Part 5 (Control Flow Pt3).
Getting Started With Ruby the Easy Way Part 6 (Methods).
Getting Started With Ruby the Easy Way Part 7 (Recursion, Scope, OOP Pt1).
Getting Started With Ruby the Easy Way Part 8 (OOP Pt2).
Getting Started With Ruby the Easy Way Part 9 (OOP Pt3).
Getting Started With Ruby the Easy Way Part 10 (OOP Pt4 and Beyond).
Control flow Pt2
The if statement is not the only tool you can use to control how Ruby executes your code. The palette is much richer. Let’s take a look what other control flow tools, or structures, you can use in Ruby.
Ternary operators
In the previous part, you’ve learned about if statements. The if statement can is very useful and powerful Although it is still very simple. However, you can take its simplicity to another level, and make your code shorter, if you want. How? You can achieve this by using something called ternary operator. Ternary operator does the same job as if statement.
It evaluates if some specific expression, or condition, is true of false. Then, it returns one value if the expression is true, and another value if the expression is false. You can think about it as a shorthand for if statement. Or, its compact version. The format of ternary operator is following one-liner: conditional ? true : false. This can be better illustrated on example.
Let’s say that you want to ask the user for a number between zero and ten. Then, you want to print a short message based on this input. Below are two examples. One uses if statement. The second uses ternary operator. As you will see, on the example below, the ternary operator example is much shorter while the result is the same. When is it better to use ternary operator instead of if statement?
Ruby developers usually use ternary operator where conditionals unnecessarily long. The code below can be a good example. Another way to use it is for variable assignment, when you want to quickly select between two values. As a rule of thumb, use this operator to select between two values with a simple conditional. Otherwise, if you are working with something more complex, if statement will be a better choice.
###
# If statement example
###
puts "Please enter a number between 0 and 10: "
# Ask user for input and convert it to an integer
i = gets.to_i
# Print message
if i > 5
puts "The number you chose is greater than 5."
else
puts "The number you chose is less than or equal to 5."
end
###
# Ternary operator example
###
puts "Please enter a number between 0 and 10: "
# Ask user for input and convert it to an integer
i = gets.to_i
# Print message using ternary operator
puts "The number you chose " + (i > 5 ? "is greater than 5." : "is less than or equal to 5.")
###
# Ternary operator and variable assignment
###
b = 5
x = b > 10 ? "bigger" : "smaller"
# the "b > 10" is the expression, or condition
# "bigger" : "smaller" are values when expression is true and false
Side note: In the example above, the one in which you ask for a number, the ternary operator is in parentheses. This is not necessary. Here, parentheses ensure that the ternary operator will not interfere with the string concatenation operators (+) surrounding it.
Logical operators
There is one more thing, related to if statements and ternary operators, you should know. You can use something called logical operators. This is handy when you want to create more complex expressions that test more than one condition. Ruby has three logical operators. These operators are “and” (&&), “or” (||) and “not” (!). The “not” is sometimes also called negation.
In Ruby, you can also use words instead of the logical operator symbols-and, or and not if you want. However, there is one thing you need to remember. Logical operator in the form of words have lower precedence than symbols. They can also sometimes make code less readable. Ruby developers usually prefer to use symbols. Now, let’s quickly take a look at each of these operators.
The and (&&) operator evaluates to true if and only if both operands, expressions on both sides of the operator, are true. Otherwise, the condition evaluates to false. The or (||) operator evaluates to true if one or both of its operands, expressions on both sides of the operator, are true. When both are false it evaluates to false.
The not (!) operator reverses, or negates, the state of a single operand. Hence the negation. The result of not true is false and not false is true. Remember that when you want to reverse, or negate, some expression you need to surround it with parentheses and put the not operator before them.
Finally, you can also use multiple conditions with logical operators, and chain them together, to check for multiple conditions. When you do this, you can use parentheses group individual conditions. This will help you keep your code readable. It will also give you more control over the order of operations.
###
# Example of and (&&) operator
###
x = 0
y = 10
z = 31
if y > x && x < z
puts "It is true."
else
puts "It is false."
end
# Outputs: It is true.
# y is bigger than x and x is smaller than z
###
# Example of or (||) operator
###
x = 111
y = 25
if x == 2 || y > 10
puts "It is true."
else
puts "It is false."
end
# Outputs: It is true.
# x is not equal to 2, but b is bigger than 10
# One of the operands is still true.
# Therefore, the condition evaluates to true.
###
# Example of not (!) operator
###
x = 5
puts !(x > 1)
# Outputs: false
###
# Example of chaining multiple conditions with logical operators
###
a = 111
b = 25
c = 5
puts (a == 2 || b > 10) || (c > 1)
# Outputs: true
Case statements
As you know, you can test for multiple conditions using the if statement, along with elsif and else. This is good and you can do a lot with. However, there is a more simplified and flexible alternative. This is where Ruby can help you with something called case expression. The case expression lets you test a specific value and execute code for multiple scenarios, or cases.
Code for each case is defined inside when statements. You can have as many when statements as you need. If you want to test multiple values, with a single when statement, you need to separate the values with commas. You can also use ranges. You will learn about ranges and how to use them in the next, fifth, part.
Lastly, you can also use the else statement. Ruby will execute the code inside if none of the when statements matches the condition. One thing you need to remember. Every case expression must be closed with the end keyword. This is similar to if statement. The last question is, when is it better to use if and when case statement?
The best scenarios when you should use if statements are when you want to determine if a conditional is true. Basically binary operations (not literally) when you have two options, one for true and one for false. Otherwise, when you need to make different decisions based on a value, use case statements.
###
# Syntax of case statement
###
case value
when value
# code to execute if "when" matches the value
end
###
# Example of case statement
###
day = "Wednesday"
case day
when "Monday"
puts "Today is Monday."
when "Tuesday"
puts "Today is Tuesday."
when "Wednesday"
puts "Today is Wednesday."
when "Thursday"
puts "Today is Thursday."
when "Friday"
puts "Today is Friday."
when "Saturday"
puts "Today is Saturday."
when "Sunday"
puts "Today is Sunday."
end
# Outputs: Today is Wednesday.
###
# Syntax of case statement with else
###
case value
when value
# code to execute if "when" matches the value
else
# code to execute if "when" doesn't match the value
end
###
# Example of case statement with else,
# multiple values and also with ranges
###
age = 16
case age
when 1, 2
puts "Baby."
when 3
puts "Toddler."
when 4..6
puts "Preschooler."
when 7..12
puts "Preschooler."
when 13..17
puts "Teenager."
else
puts "Adult."
end
# Outputs: Teenager.
While and until loops
After statements, another way to control flow in Ruby is with loops. Loops are used to execute the same block of code as many times as you want. In Ruby, there are couple of different loops you can use, four to be more specific. These loops are while, until, for and loop do. As you can guess by the names, the first two loops, the while and until are mutual opposites.
The while loop executes a block of code while its condition evaluates to true. When the condition changes and evaluate to false, the while loop will automatically stop. On the other hand, the until does the opposite of a while loop. This loop will run as long as its condition evaluates to false and stop when the condition changes and evaluate to true.
This is important to remember when you work with while and until. You have to always add code that will change the condition and stop the loop. If you forget to do this, and run the loop, it will run forever because the condition will remain true. This situation is called an infinite loop.
###
# Syntax of while loop
###
while condition
# code to execute while the condition is true
end
###
# Example of a simple while loop
# This loop will run until x is smaller than 10.
# Loop will increase the value of x every time it runs.
###
x = 0
while x < 10
puts x # print current value of <span class="hiddenGrammarError" pre="puts ">x
x</span> += 1 # increase value of x to avoid infinite loop
end
# Outputs:
# 0
# 1
# 2
# 3
# 4
# 5
# 6
# 7
# 8
# 9
###
# Syntax of until loop
###
until condition
# code to execute until the condition is false
end
x = 0
until x > 10
puts "x = #{x}"
x +=2
end
# Outputs:
# x = 0
# x = 2
# x = 4
# x = 6
# x = 8
# x = 10
For loop
The third type of loop you can use in Ruby is for loop. This loop executes a block of code for every iteration in a specific range. The for loop is composed of an empty variable and a range. Every time the loop iterates it assigns the current value of the range to the empty variable. So, during the first iteration the variable will be assigned the first value of the range.
On the second loop, it will be assigned to the new value. This will repeat until the end of the range. When you want to stop the loop, you can use break statement. If you want to skip one iteration of the loop and continue with the next one, you can use the next statement. You can also repeat the current iteration using redo statement.
Finally, when you want to restart the whole loop, and force it to start again from the beginning, you can use retry statement. The for loop is very useful when you need to loop over a specific set of values.
###
# Syntax of for loop
###
for emptyVariable in (range)
# code to execute during every iteration
end
###
# Example of for loop
# It will run seven times and print the value of i variable.
###
for i in (1..7)
puts i
end
# Outputs:
# 1
# 2
# 3
# 4
# 5
# 6
# 7
###
# Example of for loop with break statement
# Loop will stop if the variable is bigger than 4.
###
for i in 1..10
break if i > 4
puts i
end
# Outputs:
# 1
# 2
# 3
# 4
###
# Example of for loop and next statement
# Loop will output odd numbers from 0 to 10
# and skip the iteration for even numbers.
###
for i in 0..10
next if i %2 == 0 # skip even numbers
puts i # print the value of "i" variable
end
# Outputs:
# 1
# 3
# 5
# 7
# 9
Loop do
The last type of loop in Ruby is the loop do. This loop executes your code until it meets the break condition. This is important to remember. Every time you use this loop, make sure to specify condition that will stop it at some point. Otherwise, if you forget to include the break condition, the loop will run forever, just like the while and until loops.
###
# Syntax of loop do
###
loop do
# code to execute
break condition # condition that will stop the loop
end
###
# Example of loop do
###
x = 0
loop do
puts x # print value of "i" variable
x += 1 # increase the the value of "x" variable
break if x > 7 # stop the loop when "#" is bigger than 7
end
# Outputs:
# 1
# 2
# 3
# 4
# 5
# 6
# 7
Epilogue: Getting Started With Ruby the Easy Way Pt4
Congratulations! You’ve just finished another part of this series and made progress on your way to learn how to program in Ruby. Let’s do a quick recap. First, you’ve learned about what are ternary and logical operators. Next, you’ve learned about case statements. After that, you’ve learned about loops. These were the while, until, for and loop do.
In the next, fifth, part you will learn about ranges, iterators, functions and much more. This will bring you one step closer to learning how to program in Ruby and becoming a Ruby developer. Until then, review what you’ve learned today and practice on the examples above. Remember that the best way to learn programming is by writing the code by yourself.
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