Conditionals

Introduction to Julia

James Fulton

Climate informatics researcher

What are conditional expressions?

Tell our computer to do some action if a condition is met
Allow us to write code which makes its own decisions

is_raining = true


# Conditional expression
if is_raining

    println("Better get your coat")
end

Better get your coat

What are conditional expressions?

Tell our computer to do some action if a condition is met
Allow us to write code which makes its own decisions

is_raining = true 


# Conditional expression
if is_raining

println("Better get your coat")
end

Better get your coat

What are conditional expressions?

is_raining = false

# Conditional expression
if is_raining
    println("Better get your coat")
end

Multiple lines of code under the if statement

is_raining = true

if is_raining
    # This can be many lines of code

    println("The weather is awful")
    println("Better get your coat")

end

# Code below end is always run
println("Ready to go")

The weather is awful
Better get your coat
Ready to go

is_raining = false

if is_raining
    # This can be many lines of code
    println("The weather is awful")
    println("Better get your coat")
end

# Code below end is always run
println("Ready to go")

Ready to go

Comparisons

When raining:

amount_of_rain = 1.


# Use comparison
is_raining = amount_of_rain > 0


println(is_raining)

true

When dry:

amount_of_rain = 0.


# Use comparison
is_raining = amount_of_rain > 0


println(is_raining)

false

Comparisons

When raining:

amount_of_rain = 1.

# Use comparison
is_raining = amount_of_rain > 0

# Conditional expression
if is_raining
    println("Better get your coat")
end

Better get your coat

When dry:

amount_of_rain = 0.

# Use comparison
is_raining = amount_of_rain > 0

# Conditional expression
if is_raining
    println("Better get your coat")
end

Comparisons

When raining:

amount_of_rain = 1.




# Conditional expression
if amount_of_rain>0
    println("Better get your coat")
end

Better get your coat

When dry:

amount_of_rain = 0.




# Conditional expression
if amount_of_rain>0
    println("Better get your coat")
end

Other comparisons

a == b check if two values are equal

a = 1.


# Value of a is 1?
println(a==1)

true

# Data type of a is Float64?
println(typeof(a)==Float64)

true

Other comparisons

a == b check if two values are equal
a != b check if two values are not equal

a = 1.


# Value of a is not 1?
println(a!=1)

false

# Data type of a is not Float64?
println(typeof(a)!=Float64)

false

Other comparisons

a == b check if two values are equal
a != b check if two values are not equal
a > b check if a greater than b
a >= b check if greater than or equal to

a = 1.


# a is greater than 1?
println(a>1)

false

# a is greater than or equal to 1?
println(a>=1)

true

Other comparisons

a == b check if two values are equal
a != b check if two values are not equal
a > b check if a greater than b
a >= b check if greater than or equal to
a < b check if a less than b
a <= b check if less than or equal to

a = 1.


# a is less than 1?
println(a<1)

false

# a is less than or equal to 1?
println(a<=1)

true

When the condition is not met

amount_of_rain = 0.

if amount_of_rain == 0
    # Do this if conditon is met
    println("The sky looks clear")

else
    # Do this if not met
    println("Better get your coat")

end

The sky looks clear

amount_of_rain = 5.

if amount_of_rain == 0
    # Do this if conditon is met
    println("The sky looks clear")
else
    # Do this if not met
    println("Better get your coat")
end

Better get your coat

Additional conditions

amount_of_rain = 0.

if amount_of_rain == 0
    println("There is zero rain")

elseif amount_of_rain < 1
    # Add a second condition
    println("Better get your coat")

else
    println("That's a lot of rain, stay home")
end

There is zero rain

Additional conditions

amount_of_rain = 0.5

if amount_of_rain == 0
    println("There is zero rain")
elseif amount_of_rain < 1
    # Add a second condition
    println("Better get your coat")
else
    println("That's a lot of rain, stay home")
end

Better get your coat

Additional conditions

amount_of_rain = 2

if amount_of_rain == 0
    println("There is zero rain")
elseif amount_of_rain < 1
    # Add a second condition
    println("Better get your coat")
else
    println("That's a lot of rain, stay home")
end

That's a lot of rain, stay home

Multiple elseif's

amount_of_rain = 2

if amount_of_rain == 0
    println("There is zero rain")
elseif amount_of_rain < 1     # <--- many elseif conditions
    println("Better get your coat")
elseif amount_of_rain < 5     # <--- many elseif conditions
    println("You're going to need a bigger coat")
else
    println("That's a lot of rain, stay home")
end

You're going to need a bigger coat

Let's practice!

Introduction to Julia