Conditional evaluations

In the following, we start discussing control flows. Let us start with conditional statements. Recall that Julia provides booleans, that is, variables that can be either true or false. Often, an algorithm wants to react to a statement being true or false. As an example, we would like to check if a given input is correct and if it is not, print a warning message. This sentence already shows that we need an if statement, which takes the form

if condition
    # code to be run if condition is true
end

As an example, let us choose a number and check if this number is stored as a Floating Point Number (or float for short) or an Integer

number = 2

if number isa Integer
    println("This number is an integer")
end

This number is an integer

Now if this number is not an integer, we would like to print out this information. This can be done with the else statement

number  = 2.0

if number isa Integer
    println("This number is an integer")
else
    println("This number is not an integer")
end

This number is not an integer

Moreover, if we want to check whether the number is a float in case it is not an integer we can use the elseif statement

number  = 2.0

if number isa Integer
    println("This number is an integer")
elseif number isa AbstractFloat
    println("This number is a float")
else
    println("This number is neither a float nor an integer")
end

This number is a float

Note that in comparison to other programming languages, if blocks can define new variables which can be used outside of these blocks.

number  = 2.0

if number isa Integer
    info = "This number is an integer"
else
    info = "This number is not an integer"
end

println(info)

This number is not an integer