Loops

Numeric for loop

The most common and basic type of loop is the numerated for loop. This is the loop that starts at a value, increments by a certain amount (almost always 1), until it hits a certain target, running code that many times. The most common syntax for this is the one found in C/C++/Java/JavaScript:

for (int i = 0; i < 5; i++) {  // In JavaScript, replace 'int' with 'let'
    print(i);  // Print function is different for every language
}

This will result in the following output:

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> 0
> 1
> 2
> 3
> 4

To go from 1 to 5, set i to 1 initially, and make the end condition i <= 5, rather than i < 5.

This is often used to iterate through an array, like so:

​x
// Java Example
int myarr[] = {1, 2, 3, 4, 5};

// arrays start at 0, so our loop goes from 0-4 (myarr.length is 5)
for (int i = 0; i < myarr.length; i++) {
    int current_value = myarr[i];
    System.out.println(current_value);  // Java print function
}

This will output:

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> 1
> 2
> 3
> 4
> 5

While Loops

a while loop keeps running the code body until a certain condition is met.

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-- Example in Lua
local num = 0

while num < 5 do
    print(num)
    num = num + 1
end

Iterators

Some languages will have specific ways to iterate through collections like arrays. These are normally special functions called iterators.

Since they are language specific, they look different in every language.

A few examples include:

Python:

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mylist = [1, 2, 3, 4, 5]

for num in mylist:
    print(num)

Rust:

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let myvec: Vec<i32> = vec![1, 2, 3, 4, 5];

for num in myvec {
    println!("{num}");
}

Lua:

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local mytable = {1, 2, 3, 4, 5}

for i, num in pairs(mytable) do
    print(num)
end

Java/C++:

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int myarr[] = {1, 2, 3, 4, 5};

for (int x : myarr) {
    // Java
    System.out.println(x)
    // C++
    std::cout << x << std::endl;
}