Ruby Flow Control

Question 1

conditional flow

Answer 1

When you are writing programs, you want your data to make the right decisions. You want your data to do the right thing when it’s supposed to.

Question 2

conditional

Answer 2

A conditional is a fork (or many forks) in the road. Your data approaches a conditional and the conditional then tells the data where to go based on some defined parameters.

using a combination of if statements and comparison operators (, <=, >=, ==, !=, &&, ||)

basic logical structures that are defined with the reserved words if, else, elsif, and end.

conditional.rb

puts “Put in a number”
a = gets.chomp.to_i

if a == 3
  puts "a is 3"
elsif a == 4
  puts "a is 4"
else
  puts "a is neither 3, nor 4"
end

# Example 4: must use "then" keyword when using 1-line syntax
if x == 3 then puts "x is 3" end

puts “x is 3” if x == 3

Question 3

unless

Answer 3

Ruby also has a reserved word, unless. It acts as the opposite of if, so you can use it like this:

puts “x is NOT 3” unless x == 3

Question 4

boolean value

Answer 4

A boolean value is either true or false, nothing else.

Question 5

comparison operators

Answer 5

(, <=, >=, ==, !=, &&, ||)

comparison operators always return a boolean value.

Answer 6

< - The “less than” symbol. Anything to the left of the symbol has a lower value than anything to the right of the symbol.

irb :001 > 4 < 5
=> true

Question 7

>

Answer 7

>

• The “greater than” symbol. Anything to the left of the symbol has a higher value than anything to the right of the symbol.

irb :002 > 4 > 5
=> false

Question 8

<=

Answer 8

<= - The “less than or equal to” symbol. Anything to the left of the symbol is less than or equal to anything on the right.

irb :001 > 4 <= 5
=> true

Question 9

> =

Answer 9

> = - the “greater than or equal to” symbol. Anything to the left of the symbol is greater than or equal to anything on the right.

irb :002 > 5 >= 5
=> true

irb :003 > 4 >= 5
=> false

irb :004 > 4 >= 3
=> true

irb :005 > 4 >= 4
=> true

Question 10

==

Answer 10

== - The “is equal to” operator. Anything to the left of the symbol is exactly equal to anything on the right.

irb :001 > 5 == 5
=> true

irb :002 > 5 == 6
=> false

irb :003 > ‘5’ == 5
=> false

Question 11

!=

Answer 11

!= - The “not equal to” operator. Anything to the left of the symbol is not equal to anything to the right.

irb :001 > 4 != 5
=> true

irb :002 > 4 != 4
=> false

irb :003 > 4 != 156
=> true

Question 12

&&

Answer 12

&& - the “and” operator. Expressions to the left and to the right of this operator have to be both true for the entire expression to be evaluated to true.

irb :001 > (4 == 4) && (5 == 5)
=> true

irb :002 > (4 == 5) && (5 == 5)
=> false

irb :002 > (4 == 5) && (5 == 6)
=> false

Question 13

||

Answer 13

|| - the “or” operator. Either the expression to the left has to be true, or the expression to the right has to be true for the entire expression to be evaluated to true.

irb :001 > (4 == 4) || (5 == 5)
=> true

irb :002 > (4 == 5) || (5 == 5)
=> true

irb :002 > (4 == 5) || (5 == 6)
=> false

Question 14

!

Answer 14

! - the “not” operator. When you add this in front of a boolean expression it will change that boolean value to its opposite.

irb :001 > !(4 == 4)
=> false

Question 15

order of precedence

Answer 15

The following is a list of operations from highest order of precedence (top) to lowest (bottom).

<=, , >= - Comparison
==, != - Equality
&& - Logical AND
|| - Logical OR

if x && y || z
# do something
end

First the x && y statement will be executed. If that statement is true, then the program will execute the # do something code on the next line. If the x && y statement is false, then the z will be evaluated. If the z is true, the code on the next line will be evaluated. If the z is false, then the code will exit the if statement.

Question 16

ternary operator

Answer 16

Ruby has a nice option for short and concise conditional if statements. The ternary operator is a common Ruby idiom that makes a quick if/else statement easy and keeps it all on one line.

The ternary operator uses a combination of the ? and :.

irb :001 > true ? “this is true” : “this is not true”
=> “this is true”

irb :001 > false ? “this is true” : “this is not true”
=> “this is not true”

Question 17

case statement

Answer 17

A case statement has similar functionality to an if statement but with a slightly different interface.

Case statements use the reserved words case, when, else, and end.

a = 5

case a
when 5
  puts "a is 5"
when 6
  puts "a is 6"
else
  puts "a is neither 5, nor 6"
end

You can also save the result of a case statement into a variable.

a = 5

answer = case a
  when 5
    "a is 5"
  when 6
    "a is 6"
  else
    "a is neither 5, nor 6"
  end

puts answer

You don’t necessarily have to give case an argument either.

a = 5

answer = case
  when a == 5
    "a is 5"
  when a == 6
    "a is 6"
  else
    "a is neither 5, nor 6"
  end

puts answer