The IF-ELSEIF conditional

The conditional IF-ELSEIF is an evolution of the conditionals IF and IF-ELSE, which allows us to evaluate multiple conditions and execute different blocks of code based on the result of each condition.

In natural language, the loop IF-ELSEIF means:

If this happens 🡆 do this

If not, but this other thing happens 🡆 do this

(… as many ‘if not, but’ as you want …)

And if none of the above 🡆 do this

The conditional IF-ELSEIF is a way to avoid nesting, using a more comfortable and readable syntax.

Its general syntax is as follows,

if (condition1)
{
    // action to execute if condition1 is true
}
else if (condition2)
{
    // action to execute if condition1 is false, and condition2 is true
}
...
[else if] ← as many `else if` as you want
...
else
{
	// actions to execute if all previous conditions are false
}

Examples of IF-ELSEIF conditionals in different languages

Let’s look at an example of the conditional IF-ELSEIF. Suppose we have a measurement of the ambient temperature, and we want to display a result based on its value.

• If it is greater than 30º, it is hot 🔥
• If it is between 15º and 30º, the weather is nice 🌤️
• If it is less than 15º, it is cold ❄️

Many languages provide an IF-ELSEIF structure. Let’s look at some examples:

if (temperatura > 30.0)
{
	// display message 'It's hot!' 🔥
}
else if(temperatura > 15)
{
	// display message 'The weather is nice' 🌤️
}
else
{
	// display message 'It's cold!' ❄️
}

if temperatura > 30.0:
    # display message 'It's hot!' 🔥
elif temperatura > 15:
    # display message 'The weather is nice' 🌤️
else:
    # display message 'It's cold!' ❄️

If temperatura > 30.0 Then
    ' display message 'It's hot!' 🔥
ElseIf temperatura > 15 Then
    ' display message 'The weather is nice' 🌤️
Else
    ' display message 'It's cold!' ❄️
End If

The conditional IF-ELSEIF is a very powerful and readable control structure that allows us to make multiple decisions based on different conditions.

The only thing that might cause a bit of “confusion” at first is understanding that if you execute an ELSEIF, the previous conditions have already been ruled out (in the example, we saw this in the middle block. Which only executed if the temperature is between 15-30º).

But, in general, once you get the hang of it it is a quite readable structure. It is a good alternative to avoid nesting conditionals (which is something that should be reduced because they are harder to read).