Zoom Control flow

Conditional statements

Conditional statements allow to run instructions based on predicates.

Different set of instructions will be executed depending on whether the predicates return true or false.

occursin("that", "this and that")
4 < 3
a == b
a != b
2 in 1:3
3 <= 4 && 4 > 5
3 <= 4 || 4 > 5

Note that Julia possesses an inexact equality comparator which is useful to compare floating-point numbers despite computer rounding.

The function isapprox or the equivalent binary operator ≈ can be used:

0.1 + 0.2 == 0.3

false

0.1 + 0.2 ≈ 0.3

true

The negatives are the function !isapprox and ≉.

If statements

if <predicate>
    <some action>
end

• If the predicate evaluates to true, the body of the if statement gets evaluated,
• If the predicate evaluates to false, nothing happens.

function testsign1(x)
    if x >= 0
        println("x is positive")
    end
end

testsign1 (generic function with 1 method)

testsign1(3)

x is positive

testsign1(0)

x is positive

testsign1(-2)

If else statements

if <predicate>
    <some action>
else
    <some other action>
end

• If the predicate evaluates to true, <some action> is done,
• If the predicate evaluates to false, <some other action> is done.

function testsign2(x)
    if x >= 0
        println("x is positive")
    else
        println("x is negative")
    end
end

testsign2 (generic function with 1 method)

testsign2(3)

x is positive

testsign2(0)

x is positive

testsign2(-2)

x is negative

If else statements can be written in a compact format using the ternary operator:

<predicate> ? <some action> : <some other action>

<predicate> ? <action if predicate returns true> : <action if predicate returns false>

function testsign2(x)
    x >= 0 ? println("x is positive") : println("x is negative")
end

testsign2(-2)

x is negative

If elseif else statements

if <predicate1>
    <do if predicate1 true>
elseif <predicate2>
    <do if predicate1 false and predicate2 true>
else
    <do if predicate1 and predicate2 false>
end

function testsign3(x)
    if x > 0
        println("x is positive")
    elseif x == 0
        println("x is zero")
    else
        println("x is negative")
    end
end

testsign3 (generic function with 1 method)

testsign3(3)

x is positive

testsign3(0)

x is zero

testsign3(-2)

x is negative

Loops

For loops

For loops run a set of instructions for each element of an iterator:

for name = ["Paul", "Lucie", "Sophie"]
    println("Hello $name")
end

Hello Paul
Hello Lucie
Hello Sophie

for i = 1:3, j = 3:5
    println(i + j)
end

4
5
6
5
6
7
6
7
8

While loops

While loops run as long as the condition remains true:

i = 0

while i <= 10
    println(i)
    i += 1
end

0
1
2
3
4
5
6
7
8
9
10

Comments & questions