Control Flow in Ruby
Learn how to write more complex programs that can respond to user input.
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Key Concepts
Review core concepts you need to learn to master this subject
elsif Statements in Ruby
Ruby not Operator
Else statement in Ruby.
Comparison operators in Ruby.
Or operator in Ruby.
if Statement in Ruby
And operator in Ruby.
Unless statement in Ruby.
elsif Statements in Ruby
elsif Statements in Ruby
print "enter a number: "
num = gets.chomp
num = num.to_i;
if num == 5
print "number is 5"
elsif num == 10
print "number is 10"
elsif num == 11
print "number is 11"
else
print "number is something other than 5, 10, or 11"
endIn Ruby, an elsif statement can be placed between if and else statements. It allows us to check for additional conditions.
More than one elsif can be placed between if and else.
Ruby not Operator
Ruby not Operator
print "enter a number: "
num = gets.chomp
num = num.to_i;
if num == 5
print "number is 5"
elsif num == 10
print "number is 10"
elsif num == 11
print "number is 11"
else
print "number is something other than 5, 10, or 11"
endThe ! (not) operator in Ruby flips a boolean value. If a value is true then applying ! to the value changes it to false and vice versa.
Else statement in Ruby.
Else statement in Ruby.
print "enter a number: "
num = gets.chomp
num = num.to_i;
if num == 5
print "number is 5"
elsif num == 10
print "number is 10"
elsif num == 11
print "number is 11"
else
print "number is something other than 5, 10, or 11"
endIn Ruby, an if statement evaluates to either true or false. The code indented after the if portion is executed for true while the code indented after the else portion is executed for false.
Comparison operators in Ruby.
Comparison operators in Ruby.
print "enter a number: "
num = gets.chomp
num = num.to_i;
if num == 5
print "number is 5"
elsif num == 10
print "number is 10"
elsif num == 11
print "number is 11"
else
print "number is something other than 5, 10, or 11"
endThe following comparison or relational operators are used in Ruby to compare values.
> - greater than;
< - less than;
>= - greater than or equal to;
<= - less than or equal to;
== - equal to
Or operator in Ruby.
Or operator in Ruby.
print "enter a number: "
num = gets.chomp
num = num.to_i;
if num == 5
print "number is 5"
elsif num == 10
print "number is 10"
elsif num == 11
print "number is 11"
else
print "number is something other than 5, 10, or 11"
endThe || (or) operator is a logical operator which returns true if either of the expressions on left-hand side or right-hand side is true.
if Statement in Ruby
if Statement in Ruby
print "enter a number: "
num = gets.chomp
num = num.to_i;
if num == 5
print "number is 5"
elsif num == 10
print "number is 10"
elsif num == 11
print "number is 11"
else
print "number is something other than 5, 10, or 11"
endAn if statement in Ruby evaluates an expression, which returns either true or false. If the expression is true, Ruby executes the code block that follows the if whereas if the expression is false, Ruby returns nil.
In this example, the string "Your condition was true!" will print because the condition number == 10 is true.
And operator in Ruby.
And operator in Ruby.
print "enter a number: "
num = gets.chomp
num = num.to_i;
if num == 5
print "number is 5"
elsif num == 10
print "number is 10"
elsif num == 11
print "number is 11"
else
print "number is something other than 5, 10, or 11"
end&& is a logical operator in Ruby which evaluates to true only if both expressions on either side of && evaluates to true.
Unless statement in Ruby.
Unless statement in Ruby.
print "enter a number: "
num = gets.chomp
num = num.to_i;
if num == 5
print "number is 5"
elsif num == 10
print "number is 10"
elsif num == 11
print "number is 11"
else
print "number is something other than 5, 10, or 11"
endAn unless statement in Ruby is used to evaluate an expression. If the expression evaluates to false, then the code following unless is executed.
- 1You may have noticed that the kinds of programs we’ve written so far in Ruby aren’t very flexible. Sure, they can take user input, but they always produce the same result based on that input; they …
- 6In Ruby, we assign values to variables using =, the assignment operator. But if we’ve already used = for assignment, how do we check to see if two things are equal? Well, we use ==, which is a …
- 7We can also check to see if one value is less than, less than or equal to, greater than, or greater than or equal to another. Those operators look like this: * Less than: * Greater than or equal…
- 8Great work so far! You know what they say: practice makes perfect. Let’s try a few more comparators to make sure you’ve got the hang of this.
- 12You can combine boolean operators in your expressions. Combinations like (x && (y || w)) && z are not only legal expressions, but are extremely useful tools for your programs. These expression ma…
- 13Great work! So far you’ve learned: * How to use if, else, and elsif * How to use comparators / relational operators like ==, !=, , and >= * How to use boolean / logical operators like &&, ||, and !
- 14All right! You’re all on your lonesome. (Well, not quite. We’ll just leave this example here.) a = 10 b = 11 if a < b print “a is less than b!” elsif b < a print “b is less than a!” else p…
- 16Now let’s review comparators / relational operators. We’ve turned the tables a bit! Remember, comparators need to compare two values to each other to result in true or false 10 > 8 # true 8 > 10 …
- 17Home stretch! Let’s go over boolean operators. ( 1 == 1 ) && ( 2 == 2 ) # true ( 1 == 2 ) || ( 2 == 2 ) # true !( false ) # true 1. With && both comparisons on the left and right must evaluate…
- 1Now that we can direct our program using if / else statements, we can produce different results based on different user input. In this project, we’ll combine control flow with a few new Ruby strin…
- 2First, we should print a statement to prompt the user for input, then set that input to a variable using gets.chomp.
- 4All right! Time to add in a little control flow. For the if half of our branch, we want to check whether the user’s input contains an “s”. if string_to_check.include? “substring” We can do tha…
- 5Good! Now let’s complete our if statement. When we find “s”, we want Ruby to replace every instance of “s” it finds with “th”. We can do this with the .gsub! method, which stands for global **…
- 6The hard part’s over! Now we just need to let the user know if we don’t find any instances of the letter “s”.
- 7Home stretch—now we want to display the Daffy Duckified string to the user. You can do that using the string interpolation we learned earlier: my_string = “muchachos” print “Adios, #{my_string}!” #…
- 8Great work! How might you improve this project? You could: * Add an additional if statement to re-prompt the user for input if they don’t enter anything * Think about how you might account for wo…
Control Flow in Ruby
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